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diff --git a/boost/hana/fwd/or.hpp b/boost/hana/fwd/or.hpp
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+/*!
+@file
+Forward declares `boost::hana::or_`.
+
+@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_OR_HPP
+#define BOOST_HANA_FWD_OR_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Return whether any of the arguments is true-valued.
+    //! @ingroup group-Logical
+    //!
+    //! `or_` can be called with one argument or more. When called with
+    //! two arguments, `or_` uses tag-dispatching to find the right
+    //! implementation. Otherwise,
+    //! @code
+    //!     or_(x) == x
+    //!     or_(x, y, ...z) == or_(or_(x, y), z...)
+    //! @endcode
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/or.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto or_ = [](auto&& x, auto&& ...y) -> decltype(auto) {
+        return tag-dispatched;
+    };
+#else
+    template <typename L, typename = void>
+    struct or_impl : or_impl<L, when<true>> { };
+
+    struct or_t {
+        template <typename X, typename Y>
+        constexpr decltype(auto) operator()(X&& x, Y&& y) const;
+
+        template <typename X, typename ...Y>
+        constexpr decltype(auto) operator()(X&& x, Y&& ...y) const;
+    };
+
+    constexpr or_t or_{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_OR_HPP