Tree Rank + 1, T be characterized cleanly in terms of the rnnk of the tree underlying the proof. Recall that the rank is defined inductively: leaves have rank 0, and any non-leaf node with subtrees of rank r1 and r2 has rank max(ri, r2} if r1r2, and otherwise has rank r1 + 1 (= r2 + 1) (a) Show that the graph of a treelike resolution refutation using clause space s is a tree of rank s -1