+ boost::optional<TimePeriod<T> > overlap (TimePeriod<T> const & other) const {
+ T const max_from = std::max (from, other.from);
+ T const min_to = std::min (to, other.to);
+
+ if (max_from >= min_to) {
+ return boost::optional<TimePeriod<T> > ();
+ }
+
+ return TimePeriod<T> (max_from, min_to);