The vertex v is isolated if it does not belong to
any edge. Thus v is isolated if and only if deg(v) = O.
Consider the multigraph G where:
V(G) = [A,B,C,D] and
E(G) = [{A,C},{A,D},{B,B},{B,C},{C,A},{C,B},{D,B},{D,D}]
Consider the multigraph G where:
V(G) = [A,B,C,D] and
E(G) = [{A,C},{A,D},{B,B},{B,C},{C,A},{C,B},{D,B},{D,D}]

