()        *  does.  Note that the first parameter is only a hint and can        *  potentially improve the performance of the insertion process.  A bad        *  hint would cause no gains in efficiency.        *        *  For more on @a hinting, see:        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk00pt00ch00.html        *        *  Insertion requires amortized constant time.        */       template<typename... _Args>  iterator  emplace_hint(const_iterator __pos, _Args&&... __args)  { return _M_h.emplace_hint(__pos, std::forward<_Args>(__args)...); }        //@{       /**        *  @brief Attempts to insert an element into the %unordered_set.        *  @param  __x  Element to be inserted.        *  @return  A pair, of which the first element is an iterator that points        *           to the possibly inserted element, and the second is a bool        *           that is true if the element was actually inserted.        *        *  This function attempts to insert an element into the %unordered_set.        *  An %unordered_set relies on unique keys and thus an 