Figure 2

Illustrating the proof of Lemma 3. (a) Case 1: a tree that displays Qs,t∖{q0}. (b) Case 2: a tree that displays Qs,t∖{qx,y}.
Illustrating the proof of Lemma 3. (a) Case 1: a tree that displays Qs,t∖{q0}. (b) Case 2: a tree that displays Qs,t∖{qx,y}.