The Mergeable concept specifies the requirements of algorithms that merge sorted sequences into an output sequence by copying elements.
template <class I1, class I2, class Out, class R = less<>, class P1 = identity, class P2 = identity> concept bool Mergeable = InputIterator<I1> && InputIterator<I2> && WeaklyIncrementable<Out> && IndirectlyCopyable<I1, Out> && IndirectlyCopyable<I2, Out> && IndirectStrictWeakOrder<R, projected<I1, P1>, projected<I2, P2>>;