Concatenation and convex hull

rc_interval<T> concatenated(const rc_interval<T>& o) const; 
rc_interval<T>& concatenate(const rc_interval<T>& o);

These functions compute the hull of the current and a further interval, $A,B∈ RC$ such that $A,B ∈X$ for the resulting interval $X ∈ RC$ .

concatenated(const rc_interval<T>&): Return a new interval, that contains the hull of both the current and the argument supplied interval.
concatenate(const rc_interval<T>&): Expand the current interval such that it also contains the supplied interval.