Why is there no operator +/- for a bidirectional iterator?

Question

My own reasoning for it is that there is no random access and there is no way to know the bounds. But then why do we have std::advance? [EDIT] And come to think of

Answer 1

The rational for std::advance is that it should be obvious that you really intended to use it, even if it is not O(1).

You don't need a std::deadvance as you can use std::advance with a negative distance (for bidirectional iterators).