27 Iterators library [iterators]

The template parameter Iterator shall meet all the requirements of a Bidirectional Iterator.

Additionally, Iterator shall meet the requirements of a random access iterator if any of the members operator+ ([reverse.iter.op+]), operator- ([reverse.iter.op-]), operator+= ([reverse.iter.op+=]), operator-= ([reverse.iter.op-=]), operator[] ([reverse.iter.opindex]), or the non-member operators operator< ([reverse.iter.op<]), operator> ([reverse.iter.op>]),
operator<= ([reverse.iter.op<=]), operator>= ([reverse.iter.op>=]), operator- ([reverse.iter.opdiff]) or operator+ ([reverse.iter.opsum]) are referenced in a way that requires instantiation ([temp.inst]).