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diff --git a/boost/callable_traits/is_invocable.hpp b/boost/callable_traits/is_invocable.hpp
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+/*
+
+@Copyright Barrett Adair 2015-2017
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+*/
+
+#ifndef BOOST_CLBL_TRTS_IS_INVOCABLE_HPP
+#define BOOST_CLBL_TRTS_IS_INVOCABLE_HPP
+
+#include <boost/callable_traits/detail/core.hpp>
+#include <boost/callable_traits/detail/is_invocable_impl.hpp>
+
+namespace boost { namespace callable_traits {
+
+//[ is_invocable_hpp
+/*`[section:ref_is_invocable is_invocable]
+[heading Header]
+``#include <boost/callable_traits/is_invocable.hpp>``
+[heading Definition]
+*/
+
+// inherits from either std::true_type or std::false_type
+template<typename T, typename... Args>
+struct is_invocable;
+
+// inherits from either std::true_type or std::false_type
+template<typename Ret, typename T, typename... Args>
+struct is_invocable_r;
+
+//<-
+template<typename T, typename... Args>
+struct is_invocable : detail::is_invocable_impl<T, Args...>::type {
+    using type = typename detail::is_invocable_impl<T, Args...>::type;
+};
+
+template<typename Ret, typename T, typename... Args>
+struct is_invocable_r
+  : detail::is_invocable_r_impl<
+        typename detail::is_invocable_impl<T, Args...>::type, Ret, T, Args...>::type
+{
+    using type = typename detail::is_invocable_r_impl<
+        typename detail::is_invocable_impl<T, Args...>::type, Ret, T, Args...>::type;
+};
+
+#ifdef BOOST_CLBL_TRTS_DISABLE_VARIABLE_TEMPLATES
+
+template<typename T, typename... Args>
+struct is_invocable_v {
+    static_assert(std::is_same<T, detail::dummy>::value,
+        "Variable templates not supported on this compiler.");
+};
+
+template<typename Ret, typename T, typename... Args>
+struct is_invocable_r_v {
+    static_assert(std::is_same<T, detail::dummy>::value,
+        "Variable templates not supported on this compiler.");
+};
+
+#else
+//->
+// only available when variable templates are supported
+template<typename T, typename... Args>
+//<-
+BOOST_CLBL_TRAITS_INLINE_VAR
+//->
+constexpr bool is_invocable_v = //see below
+//<-
+    detail::is_invocable_impl<detail::traits<T>, Args...>::type::value;
+//->
+
+// only available when variable templates are supported
+template<typename Ret, typename T, typename... Args>
+//<-
+BOOST_CLBL_TRAITS_INLINE_VAR
+//->
+constexpr bool is_invocable_r_v = //see below
+//<-
+    detail::is_invocable_r_impl<
+        typename detail::is_invocable_impl<T, Args...>::type,
+        Ret, T, Args...>::type::value;
+#endif
+
+}} // namespace boost::callable_traits
+//->
+
+/*`
+[heading Constraints]
+* none
+
+[heading Behavior]
+* standalone c++11 implementation of c++17 `std::is_invocable`, `std::is_invocable_r`
+[note ref-qualified overloads of `operator()` with different signatures are not handled correctly yet.]
+
+[heading Example Program]
+[import ../example/is_invocable.cpp]
+[is_invocable]
+[endsect]
+*/
+//]
+
+#endif // #ifndef BOOST_CLBL_TRTS_IS_INVOCABLE_HPP