cpp/experimental/ranges/algorithm/adjacent find

@1@ Searches the range for two consecutive identical elements. Elements are compared using after being projected with. @2@ Same as, but uses as the source range, as if using  as  and  as.

Return value
An iterator to the first of the first pair of identical elements, that is, the first iterator such that both  and  are in the range  and.

If no such elements are found, an iterator that compares equal to is returned.

Complexity
If the range is nonempty, exactly applications of the predicate where  is the return value, and at most twice as many applications of the projection.