The simple graphs G_1 = (V, E_1) and G_2 = (V_2, E_2) are isomorphic if there exists a one-to-one and onto function f from V_1 to V_2 with the property that a and b are adjacent in G_1, if and only if f(a) and f(b) are adjacent in G_2, for all a and b n V_1. Use this definition (or other techniques) to show that the following pairs of graphs are isomorphic or not isomorphic