3. Question 3-Graphs
For this question, we will assume that all graphs have a vertex-set that is non-empty and finite, that is 1 ≤ |V| < ∞. Recall that we let d(v) denote the degree of a vertex in an undirected graph and din(v) and dout(v) the in-degree and out-degree of a vertex in a directed graph respectively. For this question, let n = n1 + n2 + ... + n9 denote the sum of all the digits of your student ID. State what your n is before answering the questions. If your n is even, set k = 0. If your n is odd, set k = 1. Also state what your k is before answering the questions.
For the following three statements, determine (and clearly state) whether they are true or not and prove your claim.
• If G = (V, E) is an undirected graph without self-loops with n vertices, then there can not exist two vertices v and v' in V with d(v) = k and d(v') = n - 1 - k.
• If G = (V, E) is a directed graph without self-loops that is strongly connected then for every vertex v ∈ V, we have din(v) ≥ 1 and dout(v) ≥ 1.
• If G = (V, E) is an undirected, connected graph without self-loops with n vertices, for which every vertex has an even degree, then, if we remove any edge from G, the graph is still connected.