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Groups and Monoids of Regular Graphs (And of Graphs with Bounded Degrees)

Published online by Cambridge University Press:  20 November 2018

Pavol Hell
Affiliation:
Université de Montréal, Montréal, Québec
Jaroslav Nešetřil
Affiliation:
Charles University, Prague, Czechoslovakia
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A graph X is a set V(X) (the vertices of X) with a system E(X) of 2-element subsets of V(X) (the edges of X). Let X, Y be graphs and f : V(X)V(Y) a mapping; then/ is called a homomorphism of X into F if [f(x),f(y)]E(Y) whenever [x,y]E(X). Endomorphisms, isomorphisms and automorphisms are defined in the usual manner.

Much work has been done on the subject of representing groups as groups of automorphisms of graphs (i.e., given a group G, to find a graph X such that the group of automorphisms of X is isomorphic to G). Recently, this was related to category theory, the main question being as to whether every monoid (i.e., semigroup with 1) can be represented as the monoid of endomorphisms of some graph in a given category of graphs.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 1973

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