bsl::set::lower_bound

Return an iterator providing non‐modifiable access to the first (i.e., ordered least) value_type object in this set greater‐than or equal‐to the specified key, and the past‐the‐end iterator if this set does not contain a value_type greater‐than or equal‐to key. Note that this function returns the first position before which a value_type object equivalent to key could be inserted into the ordered sequence maintained by this set, while preserving its ordering.