diff --git a/libs/algorithm/test/is_permutation.cpp b/libs/algorithm/test/is_permutation.cpp
index d9e8018c..2db24873 100644
--- a/libs/algorithm/test/is_permutation.cpp
+++ b/libs/algorithm/test/is_permutation.cpp
@@ -225,6 +225,242 @@ namespace testspr {
 				TESTSPR_BOTH_ASSERT(result);
 			}
 #endif
+
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::end(arr1),
+					sprout::begin(arr2),
+					sprout::end(arr2)
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::end(arr1),
+					sprout::begin(arr3),
+					sprout::end(arr3)
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::begin(arr1) + 5,
+					sprout::begin(arr2),
+					sprout::end(arr2) + 5
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::begin(arr1) + 5,
+					sprout::begin(arr3),
+					sprout::begin(arr3) + 5
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::end(arr1),
+					sprout::begin(arr2),
+					sprout::end(arr2),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::end(arr1),
+					sprout::begin(arr3),
+					sprout::end(arr3),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::begin(arr1) + 5,
+					sprout::begin(arr2),
+					sprout::begin(arr2) + 5,
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					sprout::begin(arr1),
+					sprout::begin(arr1) + 5,
+					sprout::begin(arr3),
+					sprout::begin(arr3) + 5,
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::end(arr1)),
+					testspr::reduct_forward(sprout::begin(arr2)),
+					testspr::reduct_forward(sprout::end(arr2))
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::end(arr1)),
+					testspr::reduct_forward(sprout::begin(arr3)),
+					testspr::reduct_forward(sprout::end(arr3))
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::begin(arr1) + 5),
+					testspr::reduct_forward(sprout::begin(arr2)),
+					testspr::reduct_forward(sprout::begin(arr2) + 5)
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::begin(arr1) + 5),
+					testspr::reduct_forward(sprout::begin(arr3)),
+					testspr::reduct_forward(sprout::begin(arr3) + 5)
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::end(arr1)),
+					testspr::reduct_forward(sprout::begin(arr2)),
+					testspr::reduct_forward(sprout::end(arr2)),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::end(arr1)),
+					testspr::reduct_forward(sprout::begin(arr3)),
+					testspr::reduct_forward(sprout::end(arr3)),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::begin(arr1) + 5),
+					testspr::reduct_forward(sprout::begin(arr2)),
+					testspr::reduct_forward(sprout::begin(arr2) + 5),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_forward(sprout::begin(arr1)),
+					testspr::reduct_forward(sprout::begin(arr1) + 5),
+					testspr::reduct_forward(sprout::begin(arr3)),
+					testspr::reduct_forward(sprout::begin(arr3) + 5),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+
+#if defined(__clang__)
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::end(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr2)),
+					testspr::reduct_random_access(sprout::end(arr2))
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::end(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr3)),
+					testspr::reduct_random_access(sprout::end(arr3))
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr1) + 5),
+					testspr::reduct_random_access(sprout::begin(arr2)),
+					testspr::reduct_random_access(sprout::begin(arr2) + 5)
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr1) + 5),
+					testspr::reduct_random_access(sprout::begin(arr3)),
+					testspr::reduct_random_access(sprout::begin(arr3) + 5)
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::end(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr2)),
+					testspr::reduct_random_access(sprout::end(arr2)),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::end(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr3)),
+					testspr::reduct_random_access(sprout::end(arr3)),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr1) + 5),
+					testspr::reduct_random_access(sprout::begin(arr2)),
+					testspr::reduct_random_access(sprout::begin(arr2) + 5),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(!result);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto result = sprout::is_permutation(
+					testspr::reduct_random_access(sprout::begin(arr1)),
+					testspr::reduct_random_access(sprout::begin(arr1) + 5),
+					testspr::reduct_random_access(sprout::begin(arr3)),
+					testspr::reduct_random_access(sprout::begin(arr3) + 5),
+					testspr::equal_to<int>()
+					);
+				TESTSPR_BOTH_ASSERT(result);
+			}
+#endif
 		}
 	}
 }	// namespace testspr
diff --git a/sprout/algorithm/equal.hpp b/sprout/algorithm/equal.hpp
index 6ae85cf6..5e808446 100644
--- a/sprout/algorithm/equal.hpp
+++ b/sprout/algorithm/equal.hpp
@@ -126,37 +126,23 @@ namespace sprout {
 
 		template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename BinaryPredicate>
 		inline SPROUT_CONSTEXPR bool
-		equal2_impl_ra_1(
+		equal2_impl_ra(
 			RandomAccessIterator1 first1, RandomAccessIterator1 last1, RandomAccessIterator2 first2, RandomAccessIterator2 last2, BinaryPredicate pred,
 			typename std::iterator_traits<RandomAccessIterator1>::difference_type pivot
 			)
 		{
 			return pivot == 0 ? pred(*first1, *first2)
-				: sprout::detail::equal2_impl_ra_1(
+				: sprout::detail::equal2_impl_ra(
 					first1, sprout::next(first1, pivot), first2, sprout::next(first2, pivot), pred,
 					pivot / 2
 					)
-					&& sprout::detail::equal2_impl_ra_1(
+					&& sprout::detail::equal2_impl_ra(
 						sprout::next(first1, pivot), last1, sprout::next(first2, pivot), last2, pred,
 						(sprout::distance(first1, last1) - pivot) / 2
 						)
 				;
 		}
 		template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename BinaryPredicate>
-		inline SPROUT_CONSTEXPR bool
-		equal2_impl_ra(
-			RandomAccessIterator1 first1, RandomAccessIterator1 last1, RandomAccessIterator2 first2, RandomAccessIterator2 last2, BinaryPredicate pred,
-			typename std::iterator_traits<RandomAccessIterator1>::difference_type size1, typename std::iterator_traits<RandomAccessIterator1>::difference_type size2
-			)
-		{
-			return size1 == size2
-				&& sprout::detail::equal2_impl_ra_1(
-					first1, last1, first2, last2, pred,
-					size1 / 2
-					)
-				;
-		}
-		template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename BinaryPredicate>
 		inline SPROUT_CONSTEXPR typename std::enable_if<
 			sprout::is_constant_distance_iterator<RandomAccessIterator1>::value && sprout::is_constant_distance_iterator<RandomAccessIterator2>::value,
 			bool
@@ -166,10 +152,12 @@ namespace sprout {
 			std::random_access_iterator_tag*
 			)
 		{
-			return sprout::detail::equal2_impl_ra(
-				first1, last1, first2, last2, pred,
-				sprout::distance(first1, last1), sprout::distance(first2, last2)
-				);
+			return sprout::distance(first1, last1) == sprout::distance(first2, last2)
+				&& sprout::detail::equal2_impl_ra(
+					first1, last1, first2, last2, pred,
+					sprout::distance(first1, last1) / 2
+					)
+				;
 		}
 
 		template<typename InputIterator1, typename InputIterator2, typename BinaryPredicate>
diff --git a/sprout/algorithm/is_permutation.hpp b/sprout/algorithm/is_permutation.hpp
index b3e8df77..1f1aebcd 100644
--- a/sprout/algorithm/is_permutation.hpp
+++ b/sprout/algorithm/is_permutation.hpp
@@ -10,7 +10,6 @@
 #include <sprout/functional/equal_to.hpp>
 #include <sprout/functional/bind2nd.hpp>
 #include <sprout/algorithm/count_if.hpp>
-#include <sprout/detail/algorithm/count_n_if.hpp>
 
 namespace sprout {
 	namespace detail {
@@ -18,19 +17,19 @@ namespace sprout {
 		inline SPROUT_CONSTEXPR bool
 		is_permutation_impl_ra(
 			RandomAccessIterator1 first1, RandomAccessIterator1 last1,
-			RandomAccessIterator2 first2, typename std::iterator_traits<RandomAccessIterator2>::difference_type d2,
+			RandomAccessIterator2 first2, RandomAccessIterator2 last2,
 			BinaryPredicate pred,
 			typename std::iterator_traits<RandomAccessIterator1>::difference_type pivot
 			)
 		{
 			return pivot == 0 ? sprout::count_if(first1, last1, sprout::bind2nd(pred, *first1))
-					<= sprout::detail::count_n_if(first2, d2, sprout::bind2nd(pred, *first1))
+					<= sprout::count_if(first2, last2, sprout::bind2nd(pred, *first1))
 				: sprout::detail::is_permutation_impl_ra(
-					first1, last1, first2, d2,
+					first1, last1, first2, last2,
 					pred, pivot / 2
 					)
 					&& sprout::detail::is_permutation_impl_ra(
-						sprout::next(first1, pivot), last1, first2, d2,
+						sprout::next(first1, pivot), last1, first2, last2,
 						pred, (sprout::distance(first1, last1) - pivot) / 2
 						)
 				;
@@ -47,7 +46,7 @@ namespace sprout {
 		{
 			return first1 == last1 ? true
 				: sprout::detail::is_permutation_impl_ra(
-					first1, last1, first2, sprout::distance(first1, last1),
+					first1, last1, first2, sprout::next(first2, sprout::distance(first1, last1)),
 					pred, sprout::distance(first1, last1) / 2
 					)
 				;
@@ -57,22 +56,22 @@ namespace sprout {
 		inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator1, bool>
 		is_permutation_impl_1(
 			sprout::pair<ForwardIterator1, bool> const& current,
-			ForwardIterator1 last1, ForwardIterator2 first2, typename std::iterator_traits<ForwardIterator2>::difference_type d2,
+			ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2,
 			BinaryPredicate pred, typename std::iterator_traits<ForwardIterator1>::difference_type n
 			)
 		{
 			typedef sprout::pair<ForwardIterator1, bool> type;
 			return !current.second || current.first == last1 ? current
 				: n == 1 ? sprout::count_if(current.first, last1, sprout::bind2nd(pred, *current.first))
-					<= sprout::detail::count_n_if(first2, d2, sprout::bind2nd(pred, *current.first))
+					<= sprout::count_if(first2, last2, sprout::bind2nd(pred, *current.first))
 					? type(sprout::next(current.first), true)
 					: type(current.first, false)
 				: sprout::detail::is_permutation_impl_1(
 					sprout::detail::is_permutation_impl_1(
 						current,
-						last1, first2, d2, pred, n / 2
+						last1, first2, last2, pred, n / 2
 						),
-					last1, first2, d2, pred, n - n / 2
+					last1, first2, last2, pred, n - n / 2
 					)
 				;
 		}
@@ -80,7 +79,7 @@ namespace sprout {
 		inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator1, bool>
 		is_permutation_impl(
 			sprout::pair<ForwardIterator1, bool> const& current,
-			ForwardIterator1 last1, ForwardIterator2 first2, typename std::iterator_traits<ForwardIterator2>::difference_type d2,
+			ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2,
 			BinaryPredicate pred, typename std::iterator_traits<ForwardIterator1>::difference_type n
 			)
 		{
@@ -88,9 +87,9 @@ namespace sprout {
 				: sprout::detail::is_permutation_impl(
 					sprout::detail::is_permutation_impl_1(
 						current,
-						last1, first2, d2, pred, n
+						last1, first2, last2, pred, n
 						),
-					last1, first2, d2, pred, n * 2
+					last1, first2, last2, pred, n * 2
 					)
 				;
 		}
@@ -102,7 +101,7 @@ namespace sprout {
 			)
 		{
 			typedef sprout::pair<ForwardIterator1, bool> type;
-			return sprout::detail::is_permutation_impl(type(first1, true), last1, first2, sprout::distance(first1, last1), pred, 1).second;
+			return sprout::detail::is_permutation_impl(type(first1, true), last1, first2, sprout::next(first2, sprout::distance(first1, last1)), pred, 1).second;
 		}
 	}	// namespace detail
 
@@ -117,12 +116,61 @@ namespace sprout {
 		typedef typename sprout::common_iterator_category<ForwardIterator1, ForwardIterator2>::type* category;
 		return sprout::detail::is_permutation(first1, last1, first2, pred, category());
 	}
-
 	template<typename ForwardIterator1, typename ForwardIterator2>
 	inline SPROUT_CONSTEXPR bool
 	is_permutation(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2) {
 		return sprout::is_permutation(first1, last1, first2, sprout::equal_to<>());
 	}
+
+	namespace detail {
+		template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename BinaryPredicate>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			sprout::is_constant_distance_iterator<RandomAccessIterator1>::value && sprout::is_constant_distance_iterator<RandomAccessIterator2>::value,
+			bool
+		>::type
+		is_permutation(
+			RandomAccessIterator1 first1, RandomAccessIterator1 last1, RandomAccessIterator2 first2, RandomAccessIterator2 last2, BinaryPredicate pred,
+			std::random_access_iterator_tag*
+			)
+		{
+			return sprout::distance(first1, last1) == sprout::distance(first2, last2)
+				&& sprout::detail::is_permutation_impl_ra(
+					first1, last1, first2, last2,
+					pred, sprout::distance(first1, last1) / 2
+					)
+				;
+		}
+
+		template<typename ForwardIterator1, typename ForwardIterator2, typename BinaryPredicate>
+		inline SPROUT_CONSTEXPR bool
+		is_permutation(
+			ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred,
+			std::forward_iterator_tag*
+			)
+		{
+			typedef sprout::pair<ForwardIterator1, bool> type;
+			return sprout::distance(first1, last1) == sprout::distance(first2, last2)
+				&& sprout::detail::is_permutation_impl(type(first1, true), last1, first2, last2, pred, 1).second
+				;
+		}
+	}	// namespace detail
+
+	// 25.2.12 Is permutation
+	//
+	//	recursion depth:
+	//		O(log N)
+	//
+	template<typename ForwardIterator1, typename ForwardIterator2, typename BinaryPredicate>
+	inline SPROUT_CONSTEXPR bool
+	is_permutation(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred) {
+		typedef typename sprout::common_iterator_category<ForwardIterator1, ForwardIterator2>::type* category;
+		return sprout::detail::is_permutation(first1, last1, first2, last2, pred, category());
+	}
+	template<typename ForwardIterator1, typename ForwardIterator2>
+	inline SPROUT_CONSTEXPR bool
+	is_permutation(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2) {
+		return sprout::is_permutation(first1, last1, first2, last2, sprout::equal_to<>());
+	}
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_ALGORITHM_IS_PERMUTATION_HPP