You never have to consider these cases explicitly. The point is that we don't need to process [m2,r], so we split only [l,m1] and apply our observation recursively.
[m2,r]
[l,m1]
You never have to consider these cases explicitly. The point is that we don't need to process
[m2,r], so we split only[l,m1]and apply our observation recursively.