Week 1-2: Graphs and Subgraphs
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چکیده
• A graph G is an ordered pair (V,E) consisting of a set V of vertices and a set E (disjoint from V ) of edges, together with an incidence function End : E → M2(V ), where M2(V ) is set of all 2-element sub-multisets of V . We usually write V = V (G), E = E(G), and End = EndG. • If e is an edge and u, v are vertices such that End(e) = {u, v}, we say that e joins u and v, or, u and v are incident with e, or, u and v are adjacent by e, and say that u, v are end-vertices of e. We say that e is a link if u 6= v and a loop if u = v. • Two edges are said to be parallel if their end-vertices are identical.
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