bsl::set::equal_range

Return a pair of iterators providing non-modifiable access to the sequence of value_type objects in this set that are equivalent to the specified key, where the first iterator is positioned at the start of the sequence, and the second is positioned one past the end of the sequence. The first returned iterator will be lower_bound(key); the second returned iterator will be upper_bound(key); and, if this set contains no value_type objects equivalent to key, then the two returned iterators will have the same value. Note that since a set maintains unique keys, the range will contain at most one element.