Method upper_bound

src/include/compact_set.h:221–225

    return iterator(this, set->lower_bound(t));
  }
  iterator upper_bound(const T& t) {
    if (!set)
      return iterator(this);
    return iterator(this, set->upper_bound(t));
  }
  const_iterator begin() const {
   if (!set)
     return const_iterator(this);