Range merge or exclusive

To check the intersections between interval [a,b] and [c,d], there are four cases (equal not shown in the figures):

    a____b
c____d

a____b
     c____d

a_______b
    c___d

   a___b
c_______d

But we can simplify these into 2 cases when check the smaller (smaller start point) interval with the bigger interval.