diff --git a/sprout/algorithm/find_difference.hpp b/sprout/algorithm/find_difference.hpp
new file mode 100644
index 00000000..6d40b075
--- /dev/null
+++ b/sprout/algorithm/find_difference.hpp
@@ -0,0 +1,115 @@
+#ifndef SPROUT_ALGORITHM_FIND_DIFFERENCE_HPP
+#define SPROUT_ALGORITHM_FIND_DIFFERENCE_HPP
+
+#include <iterator>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename InputIterator1, typename InputIterator2>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_difference_impl_check(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2
+			)
+		{
+			return sprout::tuples::get<2>(current)
+				? sprout::pair<InputIterator1, InputIterator2>(
+					sprout::tuples::get<0>(current),
+					sprout::tuples::get<1>(current)
+					)
+				: sprout::pair<InputIterator1, InputIterator2>(last1, last2)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_difference_impl_1(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 ? current
+				: n == 1 ? sprout::tuples::get<1>(current) == last2
+						? type(sprout::tuples::get<0>(current), sprout::tuples::get<1>(current), true)
+					: comp(*sprout::tuples::get<0>(current), *sprout::tuples::get<1>(current))
+						? type(sprout::tuples::get<0>(current), sprout::tuples::get<1>(current), true)
+					: comp(*sprout::tuples::get<1>(current), *sprout::tuples::get<0>(current))
+						? type(sprout::tuples::get<0>(current), sprout::next(sprout::tuples::get<1>(current)), false)
+					: type(sprout::next(sprout::tuples::get<0>(current)), sprout::next(sprout::tuples::get<1>(current)), false)
+				: sprout::detail::find_difference_impl_1(
+					sprout::detail::find_difference_impl_1(
+						current,
+						last1, last2, comp, n / 2
+						),
+					last1, last2, comp, n - n / 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_difference_impl(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 ? current
+				: sprout::detail::find_difference_impl(
+					sprout::detail::find_difference_impl_1(
+						current,
+						last1, last2, comp, n
+						),
+					last1, last2, comp, n * 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_difference(
+			InputIterator1 first1, InputIterator1 last1,
+			InputIterator2 first2, InputIterator2 last2,
+			Compare comp
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::detail::find_difference_impl_check(
+				sprout::detail::find_difference_impl(type(first1, first2, false), last1, last2, comp, 1),
+				last1, last2
+				);
+		}
+	}	// namespace detail
+
+	//
+	// find_difference
+	//
+	//	recursion depth:
+	//		O(log N)
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		return sprout::detail::find_difference(first1, last1, first2, last2, comp);
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::find_difference(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_FIND_DIFFERENCE_HPP
diff --git a/sprout/algorithm/find_intersection.hpp b/sprout/algorithm/find_intersection.hpp
new file mode 100644
index 00000000..c5f0fde0
--- /dev/null
+++ b/sprout/algorithm/find_intersection.hpp
@@ -0,0 +1,113 @@
+#ifndef SPROUT_ALGORITHM_FIND_INTERSECTION_HPP
+#define SPROUT_ALGORITHM_FIND_INTERSECTION_HPP
+
+#include <iterator>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename InputIterator1, typename InputIterator2>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_intersection_impl_check(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2
+			)
+		{
+			return sprout::tuples::get<2>(current)
+				? sprout::pair<InputIterator1, InputIterator2>(
+					sprout::tuples::get<0>(current),
+					sprout::tuples::get<1>(current)
+					)
+				: sprout::pair<InputIterator1, InputIterator2>(last1, last2)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_intersection_impl_1(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 || sprout::tuples::get<1>(current) == last2 ? current
+				: n == 1 ? comp(*sprout::tuples::get<0>(current), *sprout::tuples::get<1>(current))
+						? type(sprout::next(sprout::tuples::get<0>(current)), sprout::tuples::get<1>(current), false)
+					: comp(*sprout::tuples::get<1>(current), *sprout::tuples::get<0>(current))
+						? type(sprout::tuples::get<0>(current), sprout::next(sprout::tuples::get<1>(current)), false)
+					: type(sprout::tuples::get<0>(current), sprout::tuples::get<1>(current), true)
+				: sprout::detail::find_intersection_impl_1(
+					sprout::detail::find_intersection_impl_1(
+						current,
+						last1, last2, comp, n / 2
+						),
+					last1, last2, comp, n - n / 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_intersection_impl(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 || sprout::tuples::get<1>(current) == last2 ? current
+				: sprout::detail::find_intersection_impl(
+					sprout::detail::find_intersection_impl_1(
+						current,
+						last1, last2, comp, n
+						),
+					last1, last2, comp, n * 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_intersection(
+			InputIterator1 first1, InputIterator1 last1,
+			InputIterator2 first2, InputIterator2 last2,
+			Compare comp
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::detail::find_intersection_impl_check(
+				sprout::detail::find_intersection_impl(type(first1, first2, false), last1, last2, comp, 1),
+				last1, last2
+				);
+		}
+	}	// namespace detail
+
+	//
+	// find_intersection
+	//
+	//	recursion depth:
+	//		O(log N)
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_intersection(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		return sprout::detail::find_intersection(first1, last1, first2, last2, comp);
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_intersection(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::find_intersection(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_FIND_INTERSECTION_HPP
diff --git a/sprout/algorithm/find_symmetric_difference.hpp b/sprout/algorithm/find_symmetric_difference.hpp
new file mode 100644
index 00000000..9d1144c7
--- /dev/null
+++ b/sprout/algorithm/find_symmetric_difference.hpp
@@ -0,0 +1,103 @@
+#ifndef SPROUT_ALGORITHM_FIND_SYMMETRIC_DIFFERENCE_HPP
+#define SPROUT_ALGORITHM_FIND_SYMMETRIC_DIFFERENCE_HPP
+
+#include <iterator>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename InputIterator1, typename InputIterator2>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_symmetric_difference_impl_check(sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current) {
+			return sprout::pair<InputIterator1, InputIterator2>(
+				sprout::tuples::get<0>(current),
+				sprout::tuples::get<1>(current)
+				);
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_symmetric_difference_impl_1(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 || sprout::tuples::get<1>(current) == last2 ? current
+				: n == 1 ? comp(*sprout::tuples::get<0>(current), *sprout::tuples::get<1>(current)) || comp(*sprout::tuples::get<1>(current), *sprout::tuples::get<0>(current))
+					? type(sprout::tuples::get<0>(current), sprout::tuples::get<1>(current), true)
+					: type(sprout::next(sprout::tuples::get<0>(current)), sprout::next(sprout::tuples::get<1>(current)), false)
+				: sprout::detail::find_symmetric_difference_impl_1(
+					sprout::detail::find_symmetric_difference_impl_1(
+						current,
+						last1, last2, comp, n / 2
+						),
+					last1, last2, comp, n - n / 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::tuples::tuple<InputIterator1, InputIterator2, bool>
+		find_symmetric_difference_impl(
+			sprout::tuples::tuple<InputIterator1, InputIterator2, bool> const& current,
+			InputIterator1 last1, InputIterator2 last2, Compare comp, typename std::iterator_traits<InputIterator1>::difference_type n
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::tuples::get<2>(current) || sprout::tuples::get<0>(current) == last1 ? current
+				: sprout::detail::find_symmetric_difference_impl(
+					sprout::detail::find_symmetric_difference_impl_1(
+						current,
+						last1, last2, comp, n
+						),
+					last1, last2, comp, n * 2
+					)
+				;
+		}
+		template<typename InputIterator1, typename InputIterator2, typename Compare>
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+		find_symmetric_difference(
+			InputIterator1 first1, InputIterator1 last1,
+			InputIterator2 first2, InputIterator2 last2,
+			Compare comp
+			)
+		{
+			typedef sprout::tuples::tuple<InputIterator1, InputIterator2, bool> type;
+			return sprout::detail::find_symmetric_difference_impl_check(
+				sprout::detail::find_symmetric_difference_impl(type(first1, first2, false), last1, last2, comp, 1)
+				);
+		}
+	}	// namespace detail
+
+	//
+	// find_symmetric_difference
+	//
+	//	recursion depth:
+	//		O(log N)
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_symmetric_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		return sprout::detail::find_symmetric_difference(first1, last1, first2, last2, comp);
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	find_symmetric_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::find_symmetric_difference(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_FIND_SYMMETRIC_DIFFERENCE_HPP
diff --git a/sprout/algorithm/fixed/set_difference.hpp b/sprout/algorithm/fixed/set_difference.hpp
index b25365ec..7f5fd499 100644
--- a/sprout/algorithm/fixed/set_difference.hpp
+++ b/sprout/algorithm/fixed/set_difference.hpp
@@ -6,6 +6,7 @@
 #include <sprout/container/traits.hpp>
 #include <sprout/container/functions.hpp>
 #include <sprout/iterator/operation.hpp>
+#include <sprout/iterator/set_difference_iterator.hpp>
 #include <sprout/functional/less.hpp>
 #include <sprout/algorithm/fixed/result_of.hpp>
 #include <sprout/pit.hpp>
@@ -63,12 +64,7 @@ namespace sprout {
 								sprout::next(first1), last1, first2, last2, result, comp,
 								size, args..., *first1
 								)
-						: first2 != last2
-							? sprout::fixed::detail::set_difference_impl(
-								first1, last1, sprout::next(first2), last2, result, comp,
-								size, args...
-								)
-							: sprout::detail::container_complate(result, args...)
+						: sprout::detail::container_complate(result, args...)
 					: sprout::detail::container_complate(result, args...)
 					;
 			}
@@ -91,6 +87,24 @@ namespace sprout {
 					sprout::size(result)
 					);
 			}
+
+			template<typename InputIterator1, typename InputIterator2, typename Result, typename Compare>
+			inline SPROUT_CONSTEXPR typename std::enable_if<
+				!sprout::is_fixed_container<Result>::value,
+				typename sprout::fixed::result_of::algorithm<Result>::type
+			>::type
+			set_difference(
+				InputIterator1 first1, InputIterator1 last1,
+				InputIterator2 first2, InputIterator2 last2,
+				Result const& result, Compare comp
+				)
+			{
+				return sprout::remake<Result>(
+					result, sprout::size(result),
+					sprout::make_set_difference_iterator(first1, last1, first2, last2, comp),
+					sprout::make_set_difference_iterator(last1, last1, last2, last2, comp)
+					);
+			}
 		}	// namespace detail
 		//
 		// set_difference
diff --git a/sprout/algorithm/fixed/set_intersection.hpp b/sprout/algorithm/fixed/set_intersection.hpp
index 8567d35e..c2f19501 100644
--- a/sprout/algorithm/fixed/set_intersection.hpp
+++ b/sprout/algorithm/fixed/set_intersection.hpp
@@ -6,6 +6,7 @@
 #include <sprout/container/traits.hpp>
 #include <sprout/container/functions.hpp>
 #include <sprout/iterator/operation.hpp>
+#include <sprout/iterator/set_intersection_iterator.hpp>
 #include <sprout/functional/less.hpp>
 #include <sprout/algorithm/fixed/result_of.hpp>
 #include <sprout/pit.hpp>
@@ -59,16 +60,8 @@ namespace sprout {
 										sprout::next(first1), last1, sprout::next(first2), last2, result, comp,
 										size, args..., *first1
 										)
-							: sprout::fixed::detail::set_intersection_impl(
-								sprout::next(first1), last1, first2, last2, result, comp,
-								size, args...
-								)
-						: first2 != last2
-							? sprout::fixed::detail::set_intersection_impl(
-								first1, last1, sprout::next(first2), last2, result, comp,
-								size, args...
-								)
 							: sprout::detail::container_complate(result, args...)
+						: sprout::detail::container_complate(result, args...)
 					: sprout::detail::container_complate(result, args...)
 					;
 			}
@@ -91,6 +84,24 @@ namespace sprout {
 					sprout::size(result)
 					);
 			}
+
+			template<typename InputIterator1, typename InputIterator2, typename Result, typename Compare>
+			inline SPROUT_CONSTEXPR typename std::enable_if<
+				!sprout::is_fixed_container<Result>::value,
+				typename sprout::fixed::result_of::algorithm<Result>::type
+			>::type
+			set_intersection(
+				InputIterator1 first1, InputIterator1 last1,
+				InputIterator2 first2, InputIterator2 last2,
+				Result const& result, Compare comp
+				)
+			{
+				return sprout::remake<Result>(
+					result, sprout::size(result),
+					sprout::make_set_intersection_iterator(first1, last1, first2, last2, comp),
+					sprout::make_set_intersection_iterator(last1, last1, last2, last2, comp)
+					);
+			}
 		}	// namespace detail
 		//
 		// set_intersection
diff --git a/sprout/algorithm/fixed/set_symmetric_difference.hpp b/sprout/algorithm/fixed/set_symmetric_difference.hpp
index a95dcbcd..1bd95977 100644
--- a/sprout/algorithm/fixed/set_symmetric_difference.hpp
+++ b/sprout/algorithm/fixed/set_symmetric_difference.hpp
@@ -6,6 +6,7 @@
 #include <sprout/container/traits.hpp>
 #include <sprout/container/functions.hpp>
 #include <sprout/iterator/operation.hpp>
+#include <sprout/iterator/set_symmetric_difference_iterator.hpp>
 #include <sprout/functional/less.hpp>
 #include <sprout/algorithm/fixed/result_of.hpp>
 #include <sprout/pit.hpp>
@@ -91,6 +92,24 @@ namespace sprout {
 					sprout::size(result)
 					);
 			}
+
+			template<typename InputIterator1, typename InputIterator2, typename Result, typename Compare>
+			inline SPROUT_CONSTEXPR typename std::enable_if<
+				!sprout::is_fixed_container<Result>::value,
+				typename sprout::fixed::result_of::algorithm<Result>::type
+			>::type
+			set_symmetric_difference(
+				InputIterator1 first1, InputIterator1 last1,
+				InputIterator2 first2, InputIterator2 last2,
+				Result const& result, Compare comp
+				)
+			{
+				return sprout::remake<Result>(
+					result, sprout::size(result),
+					sprout::make_set_symmetric_difference_iterator(first1, last1, first2, last2, comp),
+					sprout::make_set_symmetric_difference_iterator(last1, last1, last2, last2, comp)
+					);
+			}
 		}	// namespace detail
 		//
 		// set_symmetric_difference
diff --git a/sprout/algorithm/next_difference.hpp b/sprout/algorithm/next_difference.hpp
new file mode 100644
index 00000000..266ca461
--- /dev/null
+++ b/sprout/algorithm/next_difference.hpp
@@ -0,0 +1,41 @@
+#ifndef SPROUT_ALGORITHM_NEXT_DIFFERENCE_HPP
+#define SPROUT_ALGORITHM_NEXT_DIFFERENCE_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_difference.hpp>
+
+namespace sprout {
+	//
+	// next_difference
+	//
+	//	recursion depth:
+	//		O(log(N1+N2))
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		typedef sprout::pair<InputIterator1, InputIterator2> type;
+		return first1 == last1 ? type(last1, last2)
+			: sprout::find_difference(sprout::next(first1), last1, first2, last2, comp)
+			;
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::next_difference(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_NEXT_DIFFERENCE_HPP
diff --git a/sprout/algorithm/next_intersection.hpp b/sprout/algorithm/next_intersection.hpp
new file mode 100644
index 00000000..4dd37054
--- /dev/null
+++ b/sprout/algorithm/next_intersection.hpp
@@ -0,0 +1,41 @@
+#ifndef SPROUT_ALGORITHM_NEXT_INTERSECTION_HPP
+#define SPROUT_ALGORITHM_NEXT_INTERSECTION_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_intersection.hpp>
+
+namespace sprout {
+	//
+	// next_intersection
+	//
+	//	recursion depth:
+	//		O(log(N1+N2))
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_intersection(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		typedef sprout::pair<InputIterator1, InputIterator2> type;
+		return first1 == last1 || first2 == last2 ? type(last1, last2)
+			: sprout::find_intersection(sprout::next(first1), last1, sprout::next(first2), last2, comp)
+			;
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_intersection(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::next_intersection(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_NEXT_INTERSECTION_HPP
diff --git a/sprout/algorithm/next_symmetric_difference.hpp b/sprout/algorithm/next_symmetric_difference.hpp
new file mode 100644
index 00000000..1e7e0473
--- /dev/null
+++ b/sprout/algorithm/next_symmetric_difference.hpp
@@ -0,0 +1,48 @@
+#ifndef SPROUT_ALGORITHM_NEXT_SYMMETRIC_DIFFERENCE_HPP
+#define SPROUT_ALGORITHM_NEXT_SYMMETRIC_DIFFERENCE_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_symmetric_difference.hpp>
+
+namespace sprout {
+	//
+	// next_symmetric_difference
+	//
+	//	recursion depth:
+	//		O(log(N1+N2))
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_symmetric_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		typedef sprout::pair<InputIterator1, InputIterator2> type;
+		return first1 != last1
+			? first2 != last2
+				? comp(*first1, *first2)
+					? sprout::find_symmetric_difference(sprout::next(first1), last1, first2, last2, comp)
+					: sprout::find_symmetric_difference(first1, last1, sprout::next(first2), last2, comp)
+				: type(sprout::next(first1), first2)
+			: first2 != last2
+				? type(first1, sprout::next(first2))
+			: type(last1, last2)
+			;
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_symmetric_difference(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::next_symmetric_difference(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_NEXT_SYMMETRIC_DIFFERENCE_HPP
diff --git a/sprout/algorithm/next_union.hpp b/sprout/algorithm/next_union.hpp
new file mode 100644
index 00000000..cffbfc0e
--- /dev/null
+++ b/sprout/algorithm/next_union.hpp
@@ -0,0 +1,49 @@
+#ifndef SPROUT_ALGORITHM_NEXT_UNION_HPP
+#define SPROUT_ALGORITHM_NEXT_UNION_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/iterator/operation.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/pair.hpp>
+
+namespace sprout {
+	//
+	// next_union
+	//
+	//	recursion depth:
+	//		O(1)
+	//
+	template<typename InputIterator1, typename InputIterator2, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_union(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2,
+		Compare comp
+		)
+	{
+		typedef sprout::pair<InputIterator1, InputIterator2> type;
+		return first1 != last1
+			? first2 != last2
+				? comp(*first1, *first2)
+					? type(sprout::next(first1), first2)
+					: comp(*first2, *first1)
+						? type(first1, sprout::next(first2))
+						: type(sprout::next(first1), sprout::next(first2))
+				: type(sprout::next(first1), first2)
+			: first2 != last2
+				? type(first1, sprout::next(first2))
+			: type(last1, last2)
+			;
+	}
+	template<typename InputIterator1, typename InputIterator2>
+	inline SPROUT_CONSTEXPR sprout::pair<InputIterator1, InputIterator2>
+	next_union(
+		InputIterator1 first1, InputIterator1 last1,
+		InputIterator2 first2, InputIterator2 last2
+		)
+	{
+		return sprout::next_union(first1, last1, first2, last2, sprout::less<>());
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ALGORITHM_NEXT_UNION_HPP
diff --git a/sprout/algorithm/non_modifying.hpp b/sprout/algorithm/non_modifying.hpp
index e05e0b98..95e2f2b1 100644
--- a/sprout/algorithm/non_modifying.hpp
+++ b/sprout/algorithm/non_modifying.hpp
@@ -46,6 +46,13 @@
 #include <sprout/algorithm/is_decreasing.hpp>
 #include <sprout/algorithm/is_strictly_increasing.hpp>
 #include <sprout/algorithm/is_strictly_decreasing.hpp>
+#include <sprout/algorithm/find_intersection.hpp>
+#include <sprout/algorithm/find_difference.hpp>
+#include <sprout/algorithm/find_symmetric_difference.hpp>
+#include <sprout/algorithm/next_union.hpp>
+#include <sprout/algorithm/next_intersection.hpp>
+#include <sprout/algorithm/next_difference.hpp>
+#include <sprout/algorithm/next_symmetric_difference.hpp>
 #include <sprout/algorithm/clamp.hpp>
 
 #endif	// #ifndef SPROUT_ALGORITHM_NON_MODIFYIING_HPP
diff --git a/sprout/algorithm/set_intersection_iterator.hpp b/sprout/algorithm/set_intersection_iterator.hpp
new file mode 100644
index 00000000..a096386e
--- /dev/null
+++ b/sprout/algorithm/set_intersection_iterator.hpp
@@ -0,0 +1,202 @@
+#ifndef SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
+#define SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
+
+#include <iterator>
+#include <utility>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/next.hpp>
+#include <sprout/iterator/type_traits/common.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/swap.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_intersection.hpp>
+#include <sprout/algorithm/next_intersection.hpp>
+
+namespace sprout {
+	//
+	// set_intersection_iterator
+	//
+	template<
+		typename LIterator, typename RIterator,
+		typename Compare = sprout::less<>
+	>
+	class set_intersection_iterator
+		: public std::iterator<
+			typename sprout::min_iterator_category<
+				typename sprout::common_iterator_category<LIterator, RIterator>::type,
+				std::forward_iterator_tag
+			>::type,
+			typename sprout::common_iterator_value_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_difference_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_pointer<LIterator, RIterator>::type,
+			typename sprout::common_iterator_reference<LIterator, RIterator>::type
+		>
+	{
+	public:
+		typedef LIterator iterator_type;
+		typedef RIterator iterator2_type;
+		typedef Compare compare_type;
+		typedef typename sprout::min_iterator_category<
+			typename sprout::common_iterator_category<LIterator, RIterator>::type,
+			std::forward_iterator_tag
+		>::type iterator_category;
+		typedef typename sprout::common_iterator_value_type<LIterator, RIterator>::type value_type;
+		typedef typename sprout::common_iterator_difference_type<LIterator, RIterator>::type difference_type;
+		typedef typename sprout::common_iterator_pointer<LIterator, RIterator>::type pointer;
+		typedef typename sprout::common_iterator_reference<LIterator, RIterator>::type reference;
+	protected:
+		typedef sprout::pair<iterator_type, iterator2_type> pair_type;
+	protected:
+		pair_type current;
+		iterator_type lst1;
+		iterator2_type lst2;
+		Compare comp;
+	private:
+		SPROUT_CONSTEXPR set_intersection_iterator(set_intersection_iterator const& other, pair_type const& next)
+			: current(next)
+			, lst1(other.lst1), lst2(other.lst2)
+			, comp(other.comp)
+		{}
+	public:
+		set_intersection_iterator()
+			: current(), lst1(), lst2(), comp()
+		{}
+		set_intersection_iterator(set_intersection_iterator const&) = default;
+		SPROUT_CONSTEXPR set_intersection_iterator(
+			iterator_type it1, iterator_type lst1,
+			iterator2_type it2, iterator2_type lst2,
+			Compare comp = Compare()
+			)
+			: current(sprout::find_intersection(it1, lst1, it2, lst2, comp))
+			, lst1(lst1), lst2(lst2)
+			, comp(comp)
+		{}
+		template<typename U, typename V, typename W>
+		SPROUT_CONSTEXPR set_intersection_iterator(set_intersection_iterator<U, V, W> const& it)
+			: current(it.base(), it.base2())
+			, lst1(it.last1()), lst2(it.last2())
+			, comp(it.compare())
+		{}
+		template<typename U, typename V, typename W>
+		set_intersection_iterator& operator=(set_intersection_iterator<U, V, W> const& it) {
+			set_intersection_iterator temp(it);
+			temp.swap(*this);
+			return *this;
+		}
+		SPROUT_CONSTEXPR iterator_type base() const {
+			return current.first;
+		}
+		SPROUT_CONSTEXPR iterator_type last1() const {
+			return lst1;
+		}
+		SPROUT_CONSTEXPR iterator2_type base2() const {
+			return current.second;
+		}
+		SPROUT_CONSTEXPR iterator2_type last2() const {
+			return lst2;
+		}
+		SPROUT_CONSTEXPR Compare compare() const {
+			return comp;
+		}
+		SPROUT_CONSTEXPR bool is_in_left() const {
+			return true;
+		}
+		SPROUT_CONSTEXPR reference operator*() const {
+			return *current.first;
+		}
+		SPROUT_CONSTEXPR pointer operator->() const {
+			return &*(*this);
+		}
+		set_intersection_iterator& operator++() {
+			current = sprout::next_intersection(current.first, lst1, current.second, lst2, comp);
+			return *this;
+		}
+		set_intersection_iterator operator++(int) {
+			set_intersection_iterator result(*this);
+			current = sprout::next_intersection(current.first, lst1, current.second, lst2, comp);
+			return result;
+		}
+		SPROUT_CONSTEXPR set_intersection_iterator next() const {
+			return set_intersection_iterator(
+				*this,
+				sprout::next_intersection(current.first, lst1, current.second, lst2, comp)
+				);
+		}
+		void swap(set_intersection_iterator& other)
+		SPROUT_NOEXCEPT_EXPR(
+			SPROUT_NOEXCEPT_EXPR(sprout::swap(current, other.current))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst1, other.lst1))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst2, other.lst2))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(comp, other.comp))
+			)
+		{
+			sprout::swap(current, other.current);
+			sprout::swap(lst1, other.lst1);
+			sprout::swap(lst2, other.lst2);
+			sprout::swap(comp, other.comp);
+		}
+	};
+
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator==(
+		sprout::set_intersection_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_intersection_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return lhs.base() == rhs.base() && lhs.base2() == rhs.base2();
+	}
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator!=(
+		sprout::set_intersection_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_intersection_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return !(lhs == rhs);
+	}
+
+	//
+	// make_set_intersection_iterator
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator, Compare>
+	make_set_intersection_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2, Compare comp) {
+		return sprout::set_intersection_iterator<LIterator, RIterator, Compare>(it1, lst1, it2, lst2, comp);
+	}
+	template<typename LIterator, typename RIterator>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator>
+	make_set_intersection_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2) {
+		return sprout::set_intersection_iterator<LIterator, RIterator>(it1, lst1, it2, lst2);
+	}
+
+	//
+	// swap
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline void
+	swap(
+		sprout::set_intersection_iterator<LIterator, RIterator, Compare>& lhs,
+		sprout::set_intersection_iterator<LIterator, RIterator, Compare>& rhs
+		)
+	SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(lhs.swap(rhs)))
+	{
+		lhs.swap(rhs);
+	}
+
+	//
+	// iterator_next
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator, Compare>
+	iterator_next(sprout::set_intersection_iterator<LIterator, RIterator, Compare> const& it) {
+		return it.next();
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
diff --git a/sprout/iterator/adaptor.hpp b/sprout/iterator/adaptor.hpp
index 307feb18..bd6ddfe3 100644
--- a/sprout/iterator/adaptor.hpp
+++ b/sprout/iterator/adaptor.hpp
@@ -16,6 +16,10 @@
 #include <sprout/iterator/joint_iterator.hpp>
 #include <sprout/iterator/alternate_iterator.hpp>
 #include <sprout/iterator/merge_iterator.hpp>
+#include <sprout/iterator/set_union_iterator.hpp>
+#include <sprout/iterator/set_intersection_iterator.hpp>
+#include <sprout/iterator/set_difference_iterator.hpp>
+#include <sprout/iterator/set_symmetric_difference_iterator.hpp>
 #include <sprout/iterator/size_enum_iterator.hpp>
 #include <sprout/iterator/bytes_iterator.hpp>
 #include <sprout/iterator/remake_iterator.hpp>
diff --git a/sprout/iterator/set_difference_iterator.hpp b/sprout/iterator/set_difference_iterator.hpp
new file mode 100644
index 00000000..8aa1ac04
--- /dev/null
+++ b/sprout/iterator/set_difference_iterator.hpp
@@ -0,0 +1,202 @@
+#ifndef SPROUT_ITERATOR_SET_DIFFERENCE_ITERATOR_HPP
+#define SPROUT_ITERATOR_SET_DIFFERENCE_ITERATOR_HPP
+
+#include <iterator>
+#include <utility>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/next.hpp>
+#include <sprout/iterator/type_traits/common.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/swap.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_difference.hpp>
+#include <sprout/algorithm/next_difference.hpp>
+
+namespace sprout {
+	//
+	// set_difference_iterator
+	//
+	template<
+		typename LIterator, typename RIterator,
+		typename Compare = sprout::less<>
+	>
+	class set_difference_iterator
+		: public std::iterator<
+			typename sprout::min_iterator_category<
+				typename sprout::common_iterator_category<LIterator, RIterator>::type,
+				std::forward_iterator_tag
+			>::type,
+			typename sprout::common_iterator_value_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_difference_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_pointer<LIterator, RIterator>::type,
+			typename sprout::common_iterator_reference<LIterator, RIterator>::type
+		>
+	{
+	public:
+		typedef LIterator iterator_type;
+		typedef RIterator iterator2_type;
+		typedef Compare compare_type;
+		typedef typename sprout::min_iterator_category<
+			typename sprout::common_iterator_category<LIterator, RIterator>::type,
+			std::forward_iterator_tag
+		>::type iterator_category;
+		typedef typename sprout::common_iterator_value_type<LIterator, RIterator>::type value_type;
+		typedef typename sprout::common_iterator_difference_type<LIterator, RIterator>::type difference_type;
+		typedef typename sprout::common_iterator_pointer<LIterator, RIterator>::type pointer;
+		typedef typename sprout::common_iterator_reference<LIterator, RIterator>::type reference;
+	protected:
+		typedef sprout::pair<iterator_type, iterator2_type> pair_type;
+	protected:
+		pair_type current;
+		iterator_type lst1;
+		iterator2_type lst2;
+		Compare comp;
+	private:
+		SPROUT_CONSTEXPR set_difference_iterator(set_difference_iterator const& other, pair_type const& next)
+			: current(next)
+			, lst1(other.lst1), lst2(other.lst2)
+			, comp(other.comp)
+		{}
+	public:
+		set_difference_iterator()
+			: current(), lst1(), lst2(), comp()
+		{}
+		set_difference_iterator(set_difference_iterator const&) = default;
+		SPROUT_CONSTEXPR set_difference_iterator(
+			iterator_type it1, iterator_type lst1,
+			iterator2_type it2, iterator2_type lst2,
+			Compare comp = Compare()
+			)
+			: current(sprout::find_difference(it1, lst1, it2, lst2, comp))
+			, lst1(lst1), lst2(lst2)
+			, comp(comp)
+		{}
+		template<typename U, typename V, typename W>
+		SPROUT_CONSTEXPR set_difference_iterator(set_difference_iterator<U, V, W> const& it)
+			: current(it.base(), it.base2())
+			, lst1(it.last1()), lst2(it.last2())
+			, comp(it.compare())
+		{}
+		template<typename U, typename V, typename W>
+		set_difference_iterator& operator=(set_difference_iterator<U, V, W> const& it) {
+			set_difference_iterator temp(it);
+			temp.swap(*this);
+			return *this;
+		}
+		SPROUT_CONSTEXPR iterator_type base() const {
+			return current.first;
+		}
+		SPROUT_CONSTEXPR iterator_type last1() const {
+			return lst1;
+		}
+		SPROUT_CONSTEXPR iterator2_type base2() const {
+			return current.second;
+		}
+		SPROUT_CONSTEXPR iterator2_type last2() const {
+			return lst2;
+		}
+		SPROUT_CONSTEXPR Compare compare() const {
+			return comp;
+		}
+		SPROUT_CONSTEXPR bool is_in_left() const {
+			return true;
+		}
+		SPROUT_CONSTEXPR reference operator*() const {
+			return *current.first;
+		}
+		SPROUT_CONSTEXPR pointer operator->() const {
+			return &*(*this);
+		}
+		set_difference_iterator& operator++() {
+			current = sprout::next_difference(current.first, lst1, current.second, lst2, comp);
+			return *this;
+		}
+		set_difference_iterator operator++(int) {
+			set_difference_iterator result(*this);
+			current = sprout::next_difference(current.first, lst1, current.second, lst2, comp);
+			return result;
+		}
+		SPROUT_CONSTEXPR set_difference_iterator next() const {
+			return set_difference_iterator(
+				*this,
+				sprout::next_difference(current.first, lst1, current.second, lst2, comp)
+				);
+		}
+		void swap(set_difference_iterator& other)
+		SPROUT_NOEXCEPT_EXPR(
+			SPROUT_NOEXCEPT_EXPR(sprout::swap(current, other.current))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst1, other.lst1))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst2, other.lst2))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(comp, other.comp))
+			)
+		{
+			sprout::swap(current, other.current);
+			sprout::swap(lst1, other.lst1);
+			sprout::swap(lst2, other.lst2);
+			sprout::swap(comp, other.comp);
+		}
+	};
+
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator==(
+		sprout::set_difference_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_difference_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return lhs.base() == rhs.base() && lhs.base2() == rhs.base2();
+	}
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator!=(
+		sprout::set_difference_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_difference_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return !(lhs == rhs);
+	}
+
+	//
+	// make_set_difference_iterator
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_difference_iterator<LIterator, RIterator, Compare>
+	make_set_difference_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2, Compare comp) {
+		return sprout::set_difference_iterator<LIterator, RIterator, Compare>(it1, lst1, it2, lst2, comp);
+	}
+	template<typename LIterator, typename RIterator>
+	inline SPROUT_CONSTEXPR sprout::set_difference_iterator<LIterator, RIterator>
+	make_set_difference_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2) {
+		return sprout::set_difference_iterator<LIterator, RIterator>(it1, lst1, it2, lst2);
+	}
+
+	//
+	// swap
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline void
+	swap(
+		sprout::set_difference_iterator<LIterator, RIterator, Compare>& lhs,
+		sprout::set_difference_iterator<LIterator, RIterator, Compare>& rhs
+		)
+	SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(lhs.swap(rhs)))
+	{
+		lhs.swap(rhs);
+	}
+
+	//
+	// iterator_next
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_difference_iterator<LIterator, RIterator, Compare>
+	iterator_next(sprout::set_difference_iterator<LIterator, RIterator, Compare> const& it) {
+		return it.next();
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ITERATOR_SET_DIFFERENCE_ITERATOR_HPP
diff --git a/sprout/iterator/set_intersection_iterator.hpp b/sprout/iterator/set_intersection_iterator.hpp
new file mode 100644
index 00000000..a096386e
--- /dev/null
+++ b/sprout/iterator/set_intersection_iterator.hpp
@@ -0,0 +1,202 @@
+#ifndef SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
+#define SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
+
+#include <iterator>
+#include <utility>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/next.hpp>
+#include <sprout/iterator/type_traits/common.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/swap.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_intersection.hpp>
+#include <sprout/algorithm/next_intersection.hpp>
+
+namespace sprout {
+	//
+	// set_intersection_iterator
+	//
+	template<
+		typename LIterator, typename RIterator,
+		typename Compare = sprout::less<>
+	>
+	class set_intersection_iterator
+		: public std::iterator<
+			typename sprout::min_iterator_category<
+				typename sprout::common_iterator_category<LIterator, RIterator>::type,
+				std::forward_iterator_tag
+			>::type,
+			typename sprout::common_iterator_value_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_difference_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_pointer<LIterator, RIterator>::type,
+			typename sprout::common_iterator_reference<LIterator, RIterator>::type
+		>
+	{
+	public:
+		typedef LIterator iterator_type;
+		typedef RIterator iterator2_type;
+		typedef Compare compare_type;
+		typedef typename sprout::min_iterator_category<
+			typename sprout::common_iterator_category<LIterator, RIterator>::type,
+			std::forward_iterator_tag
+		>::type iterator_category;
+		typedef typename sprout::common_iterator_value_type<LIterator, RIterator>::type value_type;
+		typedef typename sprout::common_iterator_difference_type<LIterator, RIterator>::type difference_type;
+		typedef typename sprout::common_iterator_pointer<LIterator, RIterator>::type pointer;
+		typedef typename sprout::common_iterator_reference<LIterator, RIterator>::type reference;
+	protected:
+		typedef sprout::pair<iterator_type, iterator2_type> pair_type;
+	protected:
+		pair_type current;
+		iterator_type lst1;
+		iterator2_type lst2;
+		Compare comp;
+	private:
+		SPROUT_CONSTEXPR set_intersection_iterator(set_intersection_iterator const& other, pair_type const& next)
+			: current(next)
+			, lst1(other.lst1), lst2(other.lst2)
+			, comp(other.comp)
+		{}
+	public:
+		set_intersection_iterator()
+			: current(), lst1(), lst2(), comp()
+		{}
+		set_intersection_iterator(set_intersection_iterator const&) = default;
+		SPROUT_CONSTEXPR set_intersection_iterator(
+			iterator_type it1, iterator_type lst1,
+			iterator2_type it2, iterator2_type lst2,
+			Compare comp = Compare()
+			)
+			: current(sprout::find_intersection(it1, lst1, it2, lst2, comp))
+			, lst1(lst1), lst2(lst2)
+			, comp(comp)
+		{}
+		template<typename U, typename V, typename W>
+		SPROUT_CONSTEXPR set_intersection_iterator(set_intersection_iterator<U, V, W> const& it)
+			: current(it.base(), it.base2())
+			, lst1(it.last1()), lst2(it.last2())
+			, comp(it.compare())
+		{}
+		template<typename U, typename V, typename W>
+		set_intersection_iterator& operator=(set_intersection_iterator<U, V, W> const& it) {
+			set_intersection_iterator temp(it);
+			temp.swap(*this);
+			return *this;
+		}
+		SPROUT_CONSTEXPR iterator_type base() const {
+			return current.first;
+		}
+		SPROUT_CONSTEXPR iterator_type last1() const {
+			return lst1;
+		}
+		SPROUT_CONSTEXPR iterator2_type base2() const {
+			return current.second;
+		}
+		SPROUT_CONSTEXPR iterator2_type last2() const {
+			return lst2;
+		}
+		SPROUT_CONSTEXPR Compare compare() const {
+			return comp;
+		}
+		SPROUT_CONSTEXPR bool is_in_left() const {
+			return true;
+		}
+		SPROUT_CONSTEXPR reference operator*() const {
+			return *current.first;
+		}
+		SPROUT_CONSTEXPR pointer operator->() const {
+			return &*(*this);
+		}
+		set_intersection_iterator& operator++() {
+			current = sprout::next_intersection(current.first, lst1, current.second, lst2, comp);
+			return *this;
+		}
+		set_intersection_iterator operator++(int) {
+			set_intersection_iterator result(*this);
+			current = sprout::next_intersection(current.first, lst1, current.second, lst2, comp);
+			return result;
+		}
+		SPROUT_CONSTEXPR set_intersection_iterator next() const {
+			return set_intersection_iterator(
+				*this,
+				sprout::next_intersection(current.first, lst1, current.second, lst2, comp)
+				);
+		}
+		void swap(set_intersection_iterator& other)
+		SPROUT_NOEXCEPT_EXPR(
+			SPROUT_NOEXCEPT_EXPR(sprout::swap(current, other.current))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst1, other.lst1))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst2, other.lst2))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(comp, other.comp))
+			)
+		{
+			sprout::swap(current, other.current);
+			sprout::swap(lst1, other.lst1);
+			sprout::swap(lst2, other.lst2);
+			sprout::swap(comp, other.comp);
+		}
+	};
+
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator==(
+		sprout::set_intersection_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_intersection_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return lhs.base() == rhs.base() && lhs.base2() == rhs.base2();
+	}
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator!=(
+		sprout::set_intersection_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_intersection_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return !(lhs == rhs);
+	}
+
+	//
+	// make_set_intersection_iterator
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator, Compare>
+	make_set_intersection_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2, Compare comp) {
+		return sprout::set_intersection_iterator<LIterator, RIterator, Compare>(it1, lst1, it2, lst2, comp);
+	}
+	template<typename LIterator, typename RIterator>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator>
+	make_set_intersection_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2) {
+		return sprout::set_intersection_iterator<LIterator, RIterator>(it1, lst1, it2, lst2);
+	}
+
+	//
+	// swap
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline void
+	swap(
+		sprout::set_intersection_iterator<LIterator, RIterator, Compare>& lhs,
+		sprout::set_intersection_iterator<LIterator, RIterator, Compare>& rhs
+		)
+	SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(lhs.swap(rhs)))
+	{
+		lhs.swap(rhs);
+	}
+
+	//
+	// iterator_next
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_intersection_iterator<LIterator, RIterator, Compare>
+	iterator_next(sprout::set_intersection_iterator<LIterator, RIterator, Compare> const& it) {
+		return it.next();
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ITERATOR_SET_INTERSECTION_ITERATOR_HPP
diff --git a/sprout/iterator/set_symmetric_difference_iterator.hpp b/sprout/iterator/set_symmetric_difference_iterator.hpp
new file mode 100644
index 00000000..b30684f8
--- /dev/null
+++ b/sprout/iterator/set_symmetric_difference_iterator.hpp
@@ -0,0 +1,270 @@
+#ifndef SPROUT_ITERATOR_SET_SYMMETRIC_DIFFERENCE_ITERATOR_HPP
+#define SPROUT_ITERATOR_SET_SYMMETRIC_DIFFERENCE_ITERATOR_HPP
+
+#include <iterator>
+#include <utility>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/iterator/next.hpp>
+#include <sprout/iterator/type_traits/common.hpp>
+#include <sprout/functional/less.hpp>
+#include <sprout/utility/swap.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/find_symmetric_difference.hpp>
+#include <sprout/algorithm/next_symmetric_difference.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<
+			typename LIterator, typename RIterator,
+			typename Compare
+		>
+		class set_symmetric_difference_iterator_impl {
+		protected:
+			typedef LIterator iterator_type;
+			typedef RIterator iterator2_type;
+			typedef Compare compare_type;
+			typedef typename sprout::min_iterator_category<
+				typename sprout::common_iterator_category<LIterator, RIterator>::type,
+				std::forward_iterator_tag
+			>::type iterator_category;
+			typedef typename sprout::common_iterator_value_type<LIterator, RIterator>::type value_type;
+			typedef typename sprout::common_iterator_difference_type<LIterator, RIterator>::type difference_type;
+			typedef typename sprout::common_iterator_pointer<LIterator, RIterator>::type pointer;
+			typedef typename sprout::common_iterator_reference<LIterator, RIterator>::type reference;
+		protected:
+			typedef sprout::pair<iterator_type, iterator2_type> pair_type;
+		protected:
+			static SPROUT_CONSTEXPR bool check_in_left(
+				iterator_type it1, iterator_type lst1,
+				iterator2_type it2, iterator2_type lst2,
+				Compare comp
+				)
+			{
+				return it1 != lst1 ? (it2 != lst2 ? comp(*it1, *it2) : true)
+					: !(it2 != lst2)
+					;
+			}
+		protected:
+			pair_type current;
+			iterator_type lst1;
+			iterator2_type lst2;
+			Compare comp;
+		protected:
+			bool in_left;
+		protected:
+			set_symmetric_difference_iterator_impl()
+				: current(), lst1(), lst2(), comp(), in_left(true)
+			{}
+			set_symmetric_difference_iterator_impl(set_symmetric_difference_iterator_impl const&) = default;
+			SPROUT_CONSTEXPR set_symmetric_difference_iterator_impl(
+				pair_type const& current,
+				iterator_type lst1, iterator2_type lst2,
+				Compare comp
+				)
+				: current(current)
+				, lst1(lst1), lst2(lst2)
+				, comp(comp)
+				, in_left(check_in_left(current.first, lst1, current.second, lst2, comp))
+			{}
+			SPROUT_CONSTEXPR set_symmetric_difference_iterator_impl(
+				pair_type const& current,
+				iterator_type lst1, iterator2_type lst2,
+				Compare comp,
+				bool in_left
+				)
+				: current(current)
+				, lst1(lst1), lst2(lst2)
+				, comp(comp)
+				, in_left(in_left)
+			{}
+		};
+	}	// namespace detail
+
+	//
+	// set_symmetric_difference_iterator
+	//
+	template<
+		typename LIterator, typename RIterator,
+		typename Compare = sprout::less<>
+	>
+	class set_symmetric_difference_iterator
+		: public std::iterator<
+			typename sprout::min_iterator_category<
+				typename sprout::common_iterator_category<LIterator, RIterator>::type,
+				std::forward_iterator_tag
+			>::type,
+			typename sprout::common_iterator_value_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_difference_type<LIterator, RIterator>::type,
+			typename sprout::common_iterator_pointer<LIterator, RIterator>::type,
+			typename sprout::common_iterator_reference<LIterator, RIterator>::type
+		>
+		, private sprout::detail::set_symmetric_difference_iterator_impl<LIterator, RIterator, Compare>
+	{
+	private:
+		typedef sprout::detail::set_symmetric_difference_iterator_impl<LIterator, RIterator, Compare> impl_type;
+	public:
+		typedef typename impl_type::iterator_type iterator_type;
+		typedef typename impl_type::iterator2_type iterator2_type;
+		typedef typename impl_type::compare_type compare_type;
+		typedef typename impl_type::iterator_category iterator_category;
+		typedef typename impl_type::value_type value_type;
+		typedef typename impl_type::difference_type difference_type;
+		typedef typename impl_type::pointer pointer;
+		typedef typename impl_type::reference reference;
+	protected:
+		typedef typename impl_type::pair_type pair_type;
+	private:
+		using impl_type::check_in_left;
+	protected:
+		using impl_type::current;
+		using impl_type::lst1;
+		using impl_type::lst2;
+		using impl_type::comp;
+	private:
+		using impl_type::in_left;
+	private:
+		SPROUT_CONSTEXPR set_symmetric_difference_iterator(set_symmetric_difference_iterator const& other, pair_type const& next)
+			: impl_type(next, other.lst1, other.lst2, other.comp)
+		{}
+	public:
+		set_symmetric_difference_iterator()
+			: impl_type()
+		{}
+		set_symmetric_difference_iterator(set_symmetric_difference_iterator const&) = default;
+		SPROUT_CONSTEXPR set_symmetric_difference_iterator(
+			iterator_type it1, iterator_type lst1,
+			iterator2_type it2, iterator2_type lst2,
+			Compare comp = Compare()
+			)
+			: impl_type(sprout::find_symmetric_difference(it1, lst1, it2, lst2, comp), lst1, lst2, comp)
+		{}
+		template<typename U, typename V, typename W>
+		SPROUT_CONSTEXPR set_symmetric_difference_iterator(set_symmetric_difference_iterator<U, V, W> const& it)
+			: impl_type(pair_type(it.base(), it.base2()), it.last1(), it.last2(), it.compare(), it.is_in_left())
+		{}
+		template<typename U, typename V, typename W>
+		set_symmetric_difference_iterator& operator=(set_symmetric_difference_iterator<U, V, W> const& it) {
+			set_symmetric_difference_iterator temp(it);
+			temp.swap(*this);
+			return *this;
+		}
+		SPROUT_CONSTEXPR iterator_type base() const {
+			return current.first;
+		}
+		SPROUT_CONSTEXPR iterator_type last1() const {
+			return lst1;
+		}
+		SPROUT_CONSTEXPR iterator2_type base2() const {
+			return current.second;
+		}
+		SPROUT_CONSTEXPR iterator2_type last2() const {
+			return lst2;
+		}
+		SPROUT_CONSTEXPR Compare compare() const {
+			return comp;
+		}
+		SPROUT_CONSTEXPR bool is_in_left() const {
+			return in_left;
+		}
+		SPROUT_CONSTEXPR reference operator*() const {
+			return is_in_left() ? *current.first : *current.second;
+		}
+		SPROUT_CONSTEXPR pointer operator->() const {
+			return &*(*this);
+		}
+		set_symmetric_difference_iterator& operator++() {
+			current = sprout::next_symmetric_difference(current.first, lst1, current.second, lst2, comp);
+			in_left = check_in_left(current.first, lst1, current.second, lst2, comp);
+			return *this;
+		}
+		set_symmetric_difference_iterator operator++(int) {
+			set_symmetric_difference_iterator result(*this);
+			current = sprout::next_symmetric_difference(current.first, lst1, current.second, lst2, comp);
+			in_left = check_in_left(current.first, lst1, current.second, lst2, comp);
+			return result;
+		}
+		SPROUT_CONSTEXPR set_symmetric_difference_iterator next() const {
+			return set_symmetric_difference_iterator(
+				*this,
+				sprout::next_symmetric_difference(current.first, lst1, current.second, lst2, comp)
+				);
+		}
+		void swap(set_symmetric_difference_iterator& other)
+		SPROUT_NOEXCEPT_EXPR(
+			SPROUT_NOEXCEPT_EXPR(sprout::swap(current, other.current))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst1, other.lst1))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst2, other.lst2))
+			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(comp, other.comp))
+			)
+		{
+			sprout::swap(current, other.current);
+			sprout::swap(lst1, other.lst1);
+			sprout::swap(lst2, other.lst2);
+			sprout::swap(comp, other.comp);
+			sprout::swap(in_left, other.in_left);
+		}
+	};
+
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator==(
+		sprout::set_symmetric_difference_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_symmetric_difference_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return lhs.base() == rhs.base() && lhs.base2() == rhs.base2();
+	}
+	template<
+		typename LIterator1, typename RIterator1, typename Compare1,
+		typename LIterator2, typename RIterator2, typename Compare2
+	>
+	inline SPROUT_CONSTEXPR bool operator!=(
+		sprout::set_symmetric_difference_iterator<LIterator1, RIterator1, Compare1> const& lhs,
+		sprout::set_symmetric_difference_iterator<LIterator2, RIterator2, Compare2> const& rhs
+		)
+	{
+		return !(lhs == rhs);
+	}
+
+	//
+	// make_set_symmetric_difference_iterator
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare>
+	make_set_symmetric_difference_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2, Compare comp) {
+		return sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare>(it1, lst1, it2, lst2, comp);
+	}
+	template<typename LIterator, typename RIterator>
+	inline SPROUT_CONSTEXPR sprout::set_symmetric_difference_iterator<LIterator, RIterator>
+	make_set_symmetric_difference_iterator(LIterator it1, LIterator lst1, RIterator it2, RIterator lst2) {
+		return sprout::set_symmetric_difference_iterator<LIterator, RIterator>(it1, lst1, it2, lst2);
+	}
+
+	//
+	// swap
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline void
+	swap(
+		sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare>& lhs,
+		sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare>& rhs
+		)
+	SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(lhs.swap(rhs)))
+	{
+		lhs.swap(rhs);
+	}
+
+	//
+	// iterator_next
+	//
+	template<typename LIterator, typename RIterator, typename Compare>
+	inline SPROUT_CONSTEXPR sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare>
+	iterator_next(sprout::set_symmetric_difference_iterator<LIterator, RIterator, Compare> const& it) {
+		return it.next();
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ITERATOR_SET_SYMMETRIC_DIFFERENCE_ITERATOR_HPP
diff --git a/sprout/iterator/set_union_iterator.hpp b/sprout/iterator/set_union_iterator.hpp
index a8bc3967..0354d8a5 100644
--- a/sprout/iterator/set_union_iterator.hpp
+++ b/sprout/iterator/set_union_iterator.hpp
@@ -7,7 +7,10 @@
 #include <sprout/config.hpp>
 #include <sprout/iterator/next.hpp>
 #include <sprout/iterator/type_traits/common.hpp>
+#include <sprout/functional/less.hpp>
 #include <sprout/utility/swap.hpp>
+#include <sprout/utility/pair.hpp>
+#include <sprout/algorithm/next_union.hpp>
 
 namespace sprout {
 	//
@@ -41,6 +44,8 @@ namespace sprout {
 		typedef typename sprout::common_iterator_difference_type<LIterator, RIterator>::type difference_type;
 		typedef typename sprout::common_iterator_pointer<LIterator, RIterator>::type pointer;
 		typedef typename sprout::common_iterator_reference<LIterator, RIterator>::type reference;
+	protected:
+		typedef sprout::pair<iterator_type, iterator2_type> pair_type;
 	private:
 		static SPROUT_CONSTEXPR bool check_in_left(
 			iterator_type it1, iterator_type lst1,
@@ -53,15 +58,22 @@ namespace sprout {
 				;
 		}
 	protected:
-		iterator_type current1;
+		pair_type current;
 		iterator_type lst1;
-		iterator2_type current2;
 		iterator2_type lst2;
 		Compare comp;
+	private:
 		bool in_left;
+	private:
+		SPROUT_CONSTEXPR set_union_iterator(set_union_iterator const& other, pair_type const& next)
+			: current(next)
+			, lst1(other.lst1), lst2(other.lst2)
+			, comp(other.comp)
+			, in_left(check_in_left(next.first, lst1, next.second, lst2, comp))
+		{}
 	public:
 		set_union_iterator()
-			: current1(), lst1(), current2(), lst2(), comp(), in_left(true)
+			: current(), lst1(), lst2(), comp(), in_left(true)
 		{}
 		set_union_iterator(set_union_iterator const&) = default;
 		SPROUT_CONSTEXPR set_union_iterator(
@@ -69,15 +81,15 @@ namespace sprout {
 			iterator2_type it2, iterator2_type lst2,
 			Compare comp = Compare()
 			)
-			: current1(it1), lst1(lst1)
-			, current2(it2), lst2(lst2)
+			: current(it1, it2)
+			, lst1(lst1), lst2(lst2)
 			, comp(comp)
 			, in_left(check_in_left(it1, lst1, it2, lst2, comp))
 		{}
 		template<typename U, typename V, typename W>
 		SPROUT_CONSTEXPR set_union_iterator(set_union_iterator<U, V, W> const& it)
-			: current1(it.base()), lst1(it.last1())
-			, current2(it.base2()), lst2(it.last2())
+			: current(it.base(), it.base2())
+			, lst1(it.last1()), lst2(it.last2())
 			, comp(it.compare())
 			, in_left(it.is_in_left())
 		{}
@@ -88,13 +100,13 @@ namespace sprout {
 			return *this;
 		}
 		SPROUT_CONSTEXPR iterator_type base() const {
-			return current1;
+			return current.first;
 		}
 		SPROUT_CONSTEXPR iterator_type last1() const {
 			return lst1;
 		}
 		SPROUT_CONSTEXPR iterator2_type base2() const {
-			return current2;
+			return current.second;
 		}
 		SPROUT_CONSTEXPR iterator2_type last2() const {
 			return lst2;
@@ -106,79 +118,38 @@ namespace sprout {
 			return in_left;
 		}
 		SPROUT_CONSTEXPR reference operator*() const {
-			return is_in_left() ? *current1 : *current2;
+			return is_in_left() ? *current.first : *current.second;
 		}
 		SPROUT_CONSTEXPR pointer operator->() const {
 			return &*(*this);
 		}
 		set_union_iterator& operator++() {
-			if (current1 != lst1) {
-				if (current2 != lst2) {
-					if (comp(*current1, *current2)) {
-						++current1;
-					} else if (comp(*current2, *current1)) {
-						++current2;
-					} else {
-						++current1;
-						++current2;
-					}
-				} else {
-					++current1;
-				}
-			} else if (current2 != lst2) {
-				++current2;
-			}
-			in_left = check_in_left(current1, lst1, current2, lst2, comp);
+			current = sprout::next_union(current.first, lst1, current.second, lst2, comp);
+			in_left = check_in_left(current.first, lst1, current.second, lst2, comp);
 			return *this;
 		}
 		set_union_iterator operator++(int) {
 			set_union_iterator result(*this);
-			if (current1 != lst1) {
-				if (current2 != lst2) {
-					if (comp(*current1, *current2)) {
-						++current1;
-					} else if (comp(*current2, *current1)) {
-						++current2;
-					} else {
-						++current1;
-						++current2;
-					}
-				} else {
-					++current1;
-				}
-			} else if (current2 != lst2) {
-				++current2;
-			}
-			in_left = check_in_left(current1, lst1, current2, lst2, comp);
+			current = sprout::next_union(current.first, lst1, current.second, lst2, comp);
+			in_left = check_in_left(current.first, lst1, current.second, lst2, comp);
 			return result;
 		}
 		SPROUT_CONSTEXPR set_union_iterator next() const {
-			return current1 != lst1
-				? current2 != lst2
-					? comp(*current1, *current2)
-						? set_union_iterator(sprout::next(current1), lst1, current2, lst2, comp)
-						: comp(*current2, *current1)
-							? set_union_iterator(current1, lst1, sprout::next(current2), lst2, comp)
-							: set_union_iterator(sprout::next(current1), lst1, sprout::next(current2), lst2, comp)
-					: set_union_iterator(sprout::next(current1), lst1, current2, lst2, comp)
-				: current2 != lst2
-					? set_union_iterator(current1, lst1, sprout::next(current2), lst2, comp)
-				: *this
-				;
+			return set_union_iterator(
+				*this,
+				sprout::next_union(current.first, lst1, current.second, lst2, comp)
+				);
 		}
 		void swap(set_union_iterator& other)
 		SPROUT_NOEXCEPT_EXPR(
-			SPROUT_NOEXCEPT_EXPR(sprout::swap(current1, other.current1))
+			SPROUT_NOEXCEPT_EXPR(sprout::swap(current, other.current))
 			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst1, other.lst1))
-			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(current2, other.current2))
 			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(lst2, other.lst2))
 			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(comp, other.comp))
-			&& SPROUT_NOEXCEPT_EXPR(sprout::swap(in_left, other.in_left))
 			)
 		{
-			sprout::swap(current1, other.current1);
+			sprout::swap(current, other.current);
 			sprout::swap(lst1, other.lst1);
-			sprout::swap(current2, other.current2);
 			sprout::swap(lst2, other.lst2);
 			sprout::swap(comp, other.comp);
 			sprout::swap(in_left, other.in_left);