Prove that if u and v are two vertices of a k-critical graph G, then N(u) 6⊆ N(v).
Let G be a k- critical graph. Assume for a contradiction that there are vertices u,v∈V(G) with u≠v and N(u)⊆N(v). Let h=χ(G−u). Consider a proper coloring of G−u with h colors. Since N(u)⊆N(v), this coloring can be extended to a proper coloring of G with h colors, by giving u the same color as v. This shows that χ(G)=χ(G−u), contradicting the assumed criticality of G.
Prove that if u and v are two vertices of a k-critical graph G, then N(u)...
need help with a and b in this graph theory question Let n >k> 1 with n even and k odd. Make a k-regular graph G by putting n vertices in a circle and connecting each vertex to the exact a) Show that for all u,v there are k internally disjoint u, v-paths (you (b) Use the previous part, even if you did not prove it, to show that the e vertex and the k 1 closest vertices on either...
PLEASE HELP Let G is a graph with 2n vertices and n^2 edges. An amicable pair of vertices is an unordered pair (u, v), such that dist(u, v) = 2. Prove that G has at least n(n − 1) amicable pairs of vertices.
Let G = (V;E) be an undirected and unweighted graph. Let S be a subset of the vertices. The graph induced on S, denoted G[S] is a graph that has vertex set S and an edge between two vertices u, v that is an element of S provided that {u,v} is an edge of G. A subset K of V is called a killer set of G if the deletion of K kills all the edges of G, that is...
Graph 2 Prove the following statements using one example for each (consider n > 5). (a) A graph G is bipartite if and only if it has no odd cycles. (b) The number of edges in a bipartite graph with n vertices is at most (n2 /2). (c) Given any two vertices u and v of a graph G, every u–v walk contains a u–v path. (d) A simple graph with n vertices and k components can have at most...
A maximal plane graph is a plane graph G = (V, E) with n ≥ 3 vertices such that if we join any two non-adjacent vertices in G, we obtain a non-plane graph. A maximal plane graph is a plane graph G = (V, E) with n-3 vertices such that if we join any two non-adjacent vertices in G, we obtain a non-plane graph. (a) Draw a maximal plane graphs on six vertices b) Show that a maximal plane graph...
Let G be a non-Hamiltonian, connected graph. For every pair of nonadjacent vertices u and v, 8(u) +8()2 k, for some k> O. Show that G contains a path of length k. Let G be a non-Hamiltonian, connected graph. For every pair of nonadjacent vertices u and v, 8(u) +8()2 k, for some k> O. Show that G contains a path of length k.
Let G be a graph with n vertices and n edges. (a) Show that G has a cycle. (b) Use part (a) to prove that if G has n vertices, k components, and n − k + 1 edges, then G has a cycle.
Prove that any graph with n vertices and at least n + k edges must have at least k + 1 cycles.
B-1 Graph coloring Given an undirected graph G (V. E), a k-coloring of G is a function c : V → {0, 1, . . . ,k-1} such that c(u)≠c(v) for every edge (u, v) ∈ E. In other words, the numbers 0.1,... k-1 represent the k colors, and adjacent vertices different colors. must havec. Let d be the maximum degree of any vertex in a graph G. Prove that we can color G with d +1 colors.
A maximal plane graph is a plane graph G = (V, E) with n ≥ 3 vertices such that if we join any two non-adjacent vertices in G, we obtain a non-plane graph. a) Draw a maximal plane graphs on six vertices. b) Show that a maximal plane graph on n points has 3n − 6 edges and 2n − 4 faces. c) A triangulation of an n-gon is a plane graph whose infinite face boundary is a convex n-gon...