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diff --git a/boost/hana/fwd/permutations.hpp b/boost/hana/fwd/permutations.hpp
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+/*!
+@file
+Forward declares `boost::hana::permutations`.
+
+@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_PERMUTATIONS_HPP
+#define BOOST_HANA_FWD_PERMUTATIONS_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Return a sequence of all the permutations of the given sequence.
+    //! @ingroup group-Sequence
+    //!
+    //! Specifically, `permutations(xs)` is a sequence whose elements are
+    //! permutations of the original sequence `xs`. The permutations are not
+    //! guaranteed to be in any specific order. Also note that the number
+    //! of permutations grows very rapidly as the length of the original
+    //! sequence increases. The growth rate is `O(length(xs)!)`; with a
+    //! sequence `xs` of length only 8, `permutations(xs)` contains over
+    //! 40 000 elements!
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/permutations.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto permutations = [](auto&& xs) {
+        return tag-dispatched;
+    };
+#else
+    template <typename S, typename = void>
+    struct permutations_impl : permutations_impl<S, when<true>> { };
+
+    struct permutations_t {
+        template <typename Xs>
+        constexpr auto operator()(Xs&& xs) const;
+    };
+
+    constexpr permutations_t permutations{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_PERMUTATIONS_HPP