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+#ifndef BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED
+#define BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED
+
+//
+//  Copyright 2015 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt
+//
+
+#include <boost/type_traits/integral_constant.hpp>
+#include <boost/type_traits/conditional.hpp>
+
+namespace boost
+{
+
+namespace type_traits_detail
+{
+
+// mp_valid
+// implementation by Bruno Dutra (by the name is_evaluable)
+
+template<template<class...> class F, class... T>
+struct mp_valid_impl
+{
+    template<template<class...> class G, class = G<T...>>
+    static boost::true_type check_s(int);
+
+    template<template<class...> class>
+    static boost::false_type check_s(...);
+
+    using type = decltype(check_s<F>(0));
+};
+
+template<template<class...> class F, class... T>
+using mp_valid = typename mp_valid_impl<F, T...>::type;
+
+// mp_defer
+
+struct mp_empty
+{
+};
+
+template<template<class...> class F, class... T> struct mp_defer_impl
+{
+    using type = F<T...>;
+};
+
+template<template<class...> class F, class... T> using mp_defer = typename boost::conditional<mp_valid<F, T...>::value, mp_defer_impl<F, T...>, mp_empty>::type;
+
+} // namespace type_traits_detail
+
+} // namespace boost
+
+#endif // #ifndef BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED