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  2. Vizing's conjecture - Wikipedia

    en.wikipedia.org/wiki/Vizing's_conjecture

    It has n 2 + 2n + 1 vertices: n 2 formed from the product of a leaf in both factors, 2n from the product of a leaf in one factor and the hub in the other factor, and one remaining vertex formed from the product of the two hubs. Each leaf-hub product vertex in G dominates exactly n of the leaf-leaf vertices, so n leaf-hub vertices are needed to ...

  3. Two-graph - Wikipedia

    en.wikipedia.org/wiki/Two-graph

    Switching {X,Y} in a graph. A two-graph is equivalent to a switching class of graphs and also to a (signed) switching class of signed complete graphs.. Switching a set of vertices in a (simple) graph means reversing the adjacencies of each pair of vertices, one in the set and the other not in the set: thus the edge set is changed so that an adjacent pair becomes nonadjacent and a nonadjacent ...

  4. Clique-sum - Wikipedia

    en.wikipedia.org/wiki/Clique-sum

    Clique-sums are important in graph structure theory, where they are used to characterize certain families of graphs as the graphs formed by clique-sums of simpler graphs. The first result of this type [2] was a theorem of Wagner (1937), who proved that the graphs that do not have a five-vertex complete graph as a minor are the 3-clique-sums of ...

  5. Homeomorphism (graph theory) - Wikipedia

    en.wikipedia.org/wiki/Homeomorphism_(graph_theory)

    In general, a subdivision of a graph G (sometimes known as an expansion [2]) is a graph resulting from the subdivision of edges in G. The subdivision of some edge e with endpoints {u,v } yields a graph containing one new vertex w, and with an edge set replacing e by two new edges, {u,w } and {w,v }. For directed edges, this operation shall ...

  6. Connectivity (graph theory) - Wikipedia

    en.wikipedia.org/wiki/Connectivity_(graph_theory)

    The edge-connectivity for a graph with at least 2 vertices is less than or equal to the minimum degree of the graph because removing all the edges that are incident to a vertex of minimum degree will disconnect that vertex from the rest of the graph. [1] For a vertex-transitive graph of degree d, we have: 2(d + 1)/3 ≤ κ(G) ≤ λ(G) = d. [11]

  7. Maximum common induced subgraph - Wikipedia

    en.wikipedia.org/.../Maximum_common_induced_subgraph

    In graph theory and theoretical computer science, a maximum common induced subgraph of two graphs G and H is a graph that is an induced subgraph of both G and H, and that has as many vertices as possible. Finding this graph is NP-hard. In the associated decision problem, the input is two graphs G and H and a number k.

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    mail.aol.com

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  9. Cartesian product of graphs - Wikipedia

    en.wikipedia.org/wiki/Cartesian_product_of_graphs

    The Cartesian product of K 2 and a path graph is a ladder graph. The Cartesian product of two path graphs is a grid graph. The Cartesian product of n edges is a hypercube: =. Thus, the Cartesian product of two hypercube graphs is another hypercube: Q i Q j = Q i+j. The Cartesian product of two median graphs is another median graph.