diff --git a/sprout/functional/bit_and.hpp b/sprout/functional/bit_and.hpp
index 195a8e6c..26ce0629 100644
--- a/sprout/functional/bit_and.hpp
+++ b/sprout/functional/bit_and.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_BIT_AND_HPP
 #define SPROUT_FUNCTIONAL_BIT_AND_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.7 bitwise operations
-	template<typename T>
+	template<typename T = void>
 	struct bit_and {
 	public:
 		typedef T first_argument_type;
@@ -16,6 +18,18 @@ namespace sprout {
 				return x & y;
 		}
 	};
+
+	template<>
+	struct bit_and<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() & std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() & std::declval<U>()))
+		{
+			return sprout::forward<T>(x) & sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_BIT_AND_HPP
diff --git a/sprout/functional/bit_not.hpp b/sprout/functional/bit_not.hpp
index 5aee9c9f..c41b3463 100644
--- a/sprout/functional/bit_not.hpp
+++ b/sprout/functional/bit_not.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_BIT_NOT_HPP
 #define SPROUT_FUNCTIONAL_BIT_NOT_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.7 bitwise operations
-	template<typename T>
+	template<typename T = void>
 	struct bit_not {
 	public:
 		typedef T argument_type;
@@ -15,6 +17,18 @@ namespace sprout {
 				return ~x;
 		}
 	};
+
+	template<>
+	struct bit_not<void> {
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR decltype(~std::declval<T>())
+		operator()(T&& x)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(~std::declval<T>()))
+		{
+			return ~sprout::forward<T>(x);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_BIT_NOT_HPP
diff --git a/sprout/functional/bit_or.hpp b/sprout/functional/bit_or.hpp
index e9cf3161..edca9b3c 100644
--- a/sprout/functional/bit_or.hpp
+++ b/sprout/functional/bit_or.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_BIT_OR_HPP
 #define SPROUT_FUNCTIONAL_BIT_OR_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.7 bitwise operations
-	template<typename T>
+	template<typename T = void>
 	struct bit_or {
 	public:
 		typedef T first_argument_type;
@@ -16,6 +18,18 @@ namespace sprout {
 				return x | y;
 		}
 	};
+
+	template<>
+	struct bit_or<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() | std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() | std::declval<U>()))
+		{
+			return sprout::forward<T>(x) | sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_BIT_OR_HPP
diff --git a/sprout/functional/bit_xor.hpp b/sprout/functional/bit_xor.hpp
index 27a289af..cc48f5f8 100644
--- a/sprout/functional/bit_xor.hpp
+++ b/sprout/functional/bit_xor.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_BIT_XOR_HPP
 #define SPROUT_FUNCTIONAL_BIT_XOR_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.7 bitwise operations
-	template<typename T>
+	template<typename T = void>
 	struct bit_xor {
 	public:
 		typedef T first_argument_type;
@@ -16,6 +18,18 @@ namespace sprout {
 				return x ^ y;
 		}
 	};
+
+	template<>
+	struct bit_xor<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() ^ std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() ^ std::declval<U>()))
+		{
+			return sprout::forward<T>(x) ^ sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_BIT_XOR_HPP
diff --git a/sprout/functional/divides.hpp b/sprout/functional/divides.hpp
index 9a72a4d7..aeecd85f 100644
--- a/sprout/functional/divides.hpp
+++ b/sprout/functional/divides.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_DEVIDES_HPP
 #define SPROUT_FUNCTIONAL_DEVIDES_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct divides {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x / y;
 		}
 	};
+
+	template<>
+	struct divides<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() / std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() / std::declval<U>()))
+		{
+			return sprout::forward<T>(x) / sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_DEVIDES_HPP
diff --git a/sprout/functional/equal_to.hpp b/sprout/functional/equal_to.hpp
index 7a32974e..38d18e6a 100644
--- a/sprout/functional/equal_to.hpp
+++ b/sprout/functional/equal_to.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_EQUAL_TO_HPP
 #define SPROUT_FUNCTIONAL_EQUAL_TO_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.5 Comparisons
-	template<typename T>
+	template<typename T = void>
 	struct equal_to {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x == y;
 		}
 	};
+
+	template<>
+	struct equal_to<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() == std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() == std::declval<U>()))
+		{
+			return sprout::forward<T>(x) == sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_EQUAL_TO_HPP
diff --git a/sprout/functional/greater.hpp b/sprout/functional/greater.hpp
index 5afe7294..b1e95bbc 100644
--- a/sprout/functional/greater.hpp
+++ b/sprout/functional/greater.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_GREATER_HPP
 #define SPROUT_FUNCTIONAL_GREATER_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.5 Comparisons
-	template<typename T>
+	template<typename T = void>
 	struct greater {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x > y;
 		}
 	};
+
+	template<>
+	struct greater<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() > std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() > std::declval<U>()))
+		{
+			return sprout::forward<T>(x) > sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_GREATER_HPP
diff --git a/sprout/functional/greater_equal.hpp b/sprout/functional/greater_equal.hpp
index 7e4b8cbe..d5edd0a4 100644
--- a/sprout/functional/greater_equal.hpp
+++ b/sprout/functional/greater_equal.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_GREATER_EQUAL_HPP
 #define SPROUT_FUNCTIONAL_GREATER_EQUAL_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.5 Comparisons
-	template<typename T>
+	template<typename T = void>
 	struct greater_equal {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x >= y;
 		}
 	};
+
+	template<>
+	struct greater_equal<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() >= std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() >= std::declval<U>()))
+		{
+			return sprout::forward<T>(x) >= sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_GREATER_EQUAL_HPP
diff --git a/sprout/functional/less.hpp b/sprout/functional/less.hpp
index aa45d7d3..befb3dca 100644
--- a/sprout/functional/less.hpp
+++ b/sprout/functional/less.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_LESS_HPP
 #define SPROUT_FUNCTIONAL_LESS_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.5 Comparisons
-	template<typename T>
+	template<typename T = void>
 	struct less {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x < y;
 		}
 	};
+
+	template<>
+	struct less<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() < std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() < std::declval<U>()))
+		{
+			return sprout::forward<T>(x) < sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_LESS_HPP
diff --git a/sprout/functional/less_equal.hpp b/sprout/functional/less_equal.hpp
index a29cb9de..91645fd4 100644
--- a/sprout/functional/less_equal.hpp
+++ b/sprout/functional/less_equal.hpp
@@ -1,7 +1,9 @@
 #ifndef SPROUT_FUNCTIONAL_LESS_EQUAL_HPP
 #define SPROUT_FUNCTIONAL_LESS_EQUAL_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
@@ -18,6 +20,18 @@ namespace sprout {
 				return x <= y;
 		}
 	};
+
+	template<>
+	struct less_equal<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() <= std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() <= std::declval<U>()))
+		{
+			return sprout::forward<T>(x) <= sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_LESS_EQUAL_HPP
diff --git a/sprout/functional/logical_and.hpp b/sprout/functional/logical_and.hpp
index 021c0682..2e301df2 100644
--- a/sprout/functional/logical_and.hpp
+++ b/sprout/functional/logical_and.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_LOGICAL_AND_HPP
 #define SPROUT_FUNCTIONAL_LOGICAL_AND_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.6 logical operations
-	template<typename T>
+	template<typename T = void>
 	struct logical_and {
 	public:
 		typedef T first_argument_type;
@@ -16,6 +18,18 @@ namespace sprout {
 				return x && y;
 		}
 	};
+
+	template<>
+	struct logical_and<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() && std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() && std::declval<U>()))
+		{
+			return sprout::forward<T>(x) && sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_LOGICAL_AND_HPP
diff --git a/sprout/functional/logical_not.hpp b/sprout/functional/logical_not.hpp
index 5e717a02..e477e860 100644
--- a/sprout/functional/logical_not.hpp
+++ b/sprout/functional/logical_not.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_LOGICAL_NOT_HPP
 #define SPROUT_FUNCTIONAL_LOGICAL_NOT_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.6 logical operations
-	template<typename T>
+	template<typename T = void>
 	struct logical_not {
 	public:
 		typedef T argument_type;
@@ -15,6 +17,18 @@ namespace sprout {
 				return !x;
 		}
 	};
+
+	template<>
+	struct logical_not<void> {
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR decltype(!std::declval<T>())
+		operator()(T&& x)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(!std::declval<T>()))
+		{
+			return !sprout::forward<T>(x);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_LOGICAL_NOT_HPP
diff --git a/sprout/functional/logical_or.hpp b/sprout/functional/logical_or.hpp
index f0e0045c..1bdf20b8 100644
--- a/sprout/functional/logical_or.hpp
+++ b/sprout/functional/logical_or.hpp
@@ -1,11 +1,13 @@
 #ifndef SPROUT_FUNCTIONAL_LOGICAL_OR_HPP
 #define SPROUT_FUNCTIONAL_LOGICAL_OR_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// 20.8.6 logical operations
-	template<typename T>
+	template<typename T = void>
 	struct logical_or {
 	public:
 		typedef T first_argument_type;
@@ -16,6 +18,18 @@ namespace sprout {
 				return x || y;
 		}
 	};
+
+	template<>
+	struct logical_or<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() || std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() || std::declval<U>()))
+		{
+			return sprout::forward<T>(x) || sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_LOGICAL_OR_HPP
diff --git a/sprout/functional/minus.hpp b/sprout/functional/minus.hpp
index 8c219d60..e37bc042 100644
--- a/sprout/functional/minus.hpp
+++ b/sprout/functional/minus.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_MINUS_HPP
 #define SPROUT_FUNCTIONAL_MINUS_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct minus {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x - y;
 		}
 	};
+
+	template<>
+	struct minus<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() - std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() - std::declval<U>()))
+		{
+			return sprout::forward<T>(x) - sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_MINUS_HPP
diff --git a/sprout/functional/modulus.hpp b/sprout/functional/modulus.hpp
index 5a6decb5..3e0c2d39 100644
--- a/sprout/functional/modulus.hpp
+++ b/sprout/functional/modulus.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_MODULUS_HPP
 #define SPROUT_FUNCTIONAL_X_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct modulus {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x % y;
 		}
 	};
+
+	template<>
+	struct modulus<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() % std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() % std::declval<U>()))
+		{
+			return sprout::forward<T>(x) % sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_MODULUS_HPP
diff --git a/sprout/functional/multiplies.hpp b/sprout/functional/multiplies.hpp
index d91988cd..257b124f 100644
--- a/sprout/functional/multiplies.hpp
+++ b/sprout/functional/multiplies.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_MULTIPLIES_HPP
 #define SPROUT_FUNCTIONAL_MULTIPLIES_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct multiplies {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x * y;
 		}
 	};
+
+	template<>
+	struct multiplies<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() * std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() * std::declval<U>()))
+		{
+			return sprout::forward<T>(x) * sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_MULTIPLIES_HPP
diff --git a/sprout/functional/negate.hpp b/sprout/functional/negate.hpp
index c0d59868..7ff5c2ff 100644
--- a/sprout/functional/negate.hpp
+++ b/sprout/functional/negate.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_NEGATE_HPP
 #define SPROUT_FUNCTIONAL_NEGATE_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct negate {
 	public:
 		typedef T argument_type;
@@ -17,6 +19,18 @@ namespace sprout {
 				return -x;
 		}
 	};
+
+	template<>
+	struct negate<void> {
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR decltype(-std::declval<T>())
+		operator()(T&& x)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(-std::declval<T>()))
+		{
+			return -sprout::forward<T>(x);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_NEGATE_HPP
diff --git a/sprout/functional/not_equal_to.hpp b/sprout/functional/not_equal_to.hpp
index bfb4ec6d..7634b668 100644
--- a/sprout/functional/not_equal_to.hpp
+++ b/sprout/functional/not_equal_to.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_NOT_EQUAL_TO_HPP
 #define SPROUT_FUNCTIONAL_NOT_EQUAL_TO_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.5 Comparisons
-	template<typename T>
+	template<typename T = void>
 	struct not_equal_to {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 				return x != y;
 		}
 	};
+
+	template<>
+	struct not_equal_to<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() != std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() != std::declval<U>()))
+		{
+			return sprout::forward<T>(x) != sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_NOT_EQUAL_TO_HPP
diff --git a/sprout/functional/plus.hpp b/sprout/functional/plus.hpp
index e511d892..70e81374 100644
--- a/sprout/functional/plus.hpp
+++ b/sprout/functional/plus.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_PLUS_HPP
 #define SPROUT_FUNCTIONAL_PLUS_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct plus {
 	public:
 		typedef T first_argument_type;
@@ -18,6 +20,18 @@ namespace sprout {
 			return x + y;
 		}
 	};
+
+	template<>
+	struct plus<void> {
+	public:
+		template<typename T, typename U>
+		SPROUT_CONSTEXPR decltype(std::declval<T>() + std::declval<U>())
+		operator()(T&& x, U&& y)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<T>() + std::declval<U>()))
+		{
+			return sprout::forward<T>(x) + sprout::forward<U>(y);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_PLUS_HPP
diff --git a/sprout/functional/polymorphic/functor.hpp b/sprout/functional/polymorphic/functor.hpp
index 17871cb4..20991784 100644
--- a/sprout/functional/polymorphic/functor.hpp
+++ b/sprout/functional/polymorphic/functor.hpp
@@ -7,6 +7,7 @@
 #include <sprout/functional/polymorphic/logical.hpp>
 #include <sprout/functional/polymorphic/bitwise.hpp>
 #include <sprout/functional/polymorphic/inc_dec.hpp>
+#include <sprout/functional/polymorphic/reference.hpp>
 #include <sprout/functional/polymorphic/assignment.hpp>
 #include <sprout/functional/polymorphic/members.hpp>
 #include <sprout/functional/polymorphic/various.hpp>
diff --git a/sprout/functional/posite.hpp b/sprout/functional/posite.hpp
index 81c92778..c7c10ff8 100644
--- a/sprout/functional/posite.hpp
+++ b/sprout/functional/posite.hpp
@@ -1,13 +1,15 @@
 #ifndef SPROUT_FUNCTIONAL_POSITE_HPP
 #define SPROUT_FUNCTIONAL_POSITE_HPP
 
+#include <utility>
 #include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
 	// 20.8.4 Arithmetic operations
-	template<typename T>
+	template<typename T = void>
 	struct posite {
 	public:
 		typedef T argument_type;
@@ -17,6 +19,18 @@ namespace sprout {
 				return +x;
 		}
 	};
+
+	template<>
+	struct posite<void> {
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR decltype(+std::declval<T>())
+		operator()(T&& x)
+		const SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(+std::declval<T>()))
+		{
+			return +sprout::forward<T>(x);
+		}
+	};
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_FUNCTIONAL_POSITE_HPP