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Comptes Rendus Mathématique
Volume 341, n° 1
pages 1-4 (juillet 2005)
Doi : 10.1016/j.crma.2005.05.021
Received : 27 April 2005 ;  accepted : 4 May 2005
Functional graphs
Graphes fonctionnels

Amine El Sahili
Lebanese university I, El hadas, Beyrout, Lebanon 


A graph G is said to be a functional graph if there exist two mappings f and g from   into a set F such that xy is an edge in G whenever   or  . Chvátal and Ebenegger proved that recognizing functional graphs is an NP-complete problem. Using the compactness theorem, we prove that if G is an infinite graph such that any finite subgraph of G is a functional graph, then G is a functional graph. We give an elementary proof of this fact in the infinite countable case. In the finite case, we prove that for n large enough, any graph of girth n containing at most   vertices is a functional graph. It will be shown by an example that this bound is the best possible. To cite this article: A. El Sahili, C. R. Acad. Sci. Paris, Ser. I 341 (2005).

The full text of this article is available in PDF format.

Un graphe G est dit graphe fonctionnel sʼil existe deux applications f et g de   dans un ensemble F telles que xy est une arête de G si et seulement si   ou  . Chvátal et Ebenegger ont prouvé que le problème de reconnaissance des graphes fonctionnels est NP-complet. En utilisant le théorème de compacité, nous prouvons que si G est un graphe infini tel que tout sous-graphe fini de G est fonctionnel, alors G est fonctionnel. Nous donnons une preuve élémentaire de ce fait dans le cas dénombrable. Dans le cas fini, nous prouvons que pour n suffisamment grand, tout graphe sans cycle dʼordre plus petit que n et contenant au plus   sommets est un graphe fonctionnel. Il sera montré à lʼaide dʼun exemple que   est la meilleure borne possible. Pour citer cet article : A. El Sahili, C. R. Acad. Sci. Paris, Ser. I 341 (2005).

The full text of this article is available in PDF format.

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