1. Prove, disprove (give a counterexample, highlight the incorrectness or give the correct answer) or complete a proof. (c) Let G be a dag, and let t be the vertex that becomes finished during an execution of a depth-first search. Then t is a sink. Proposition. Let tree l be the result of applying depth-first search to a connected graph G. Then a non-root v of T is a cut-vertex of G if and only if v has a child w such that no descendant of wis joined to a proper ancestor of v by a non-tree edge. Notation: Let low(w) denote the smaller of dfnumber(w) and the smallest dfnumber among all vertices joined by a non-tree edge to some descendant of w