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diff --git a/boost/hana/fwd/core/default.hpp b/boost/hana/fwd/core/default.hpp
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+/*!
+@file
+Forward declares `boost::hana::default_` and `boost::hana::is_default`.
+
+@copyright Louis Dionne 2013-2016
+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_HANA_FWD_CORE_DEFAULT_HPP
+#define BOOST_HANA_FWD_CORE_DEFAULT_HPP
+
+#include <boost/hana/config.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @ingroup group-core
+    //! Mark a tag-dispatched method implementation as a default implementation.
+    //!
+    //! When defining a new concept with tag-dispatched methods, it is
+    //! sometimes possible to provide a default implementation for some
+    //! method(s). Making `default_` a base class of such a default
+    //! implementation makes it possible to detect whether the method
+    //! was dispatched to the default implementation afterwards.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/core/default.cpp
+    struct default_ { };
+
+    //! @ingroup group-core
+    //! Returns whether a tag-dispatched method implementation is a default
+    //! implementation.
+    //!
+    //! Given a tag-dispatched method implementation `method_impl<T...>`,
+    //! `is_default<method_impl<T...>>` returns whether `method_impl<T...>`
+    //! is a default implementation. Note that if there is no default
+    //! implementation for the method, then `is_default` should not be
+    //! used unless a static assertion saying that "the method is not
+    //! implemented" is acceptable.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/core/default.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    template <typename Method>
+    struct is_default { see documentation };
+#else
+    template <typename T, typename = void>
+    struct is_default;
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_CORE_DEFAULT_HPP