Classes of graphs definable by graph algebra identities or quasi-identities
In the category of symmetric graphs there are exactly five closed tensor products. If we omit the requirement of units, we obtain twelve more.
La généralisation des nombres chromatiques de Stahl a été un premier thème de travail avec François et a abouti à l’introduction de la notion de colorations généralisées et leurs nombres chromatiques associés, notées . Cette nouvelle notion a permis d’une part, d’infirmer avec Payan une conjecture posée par Brigham et Dutton, et d’autre part, d’étendre de manière naturelle la formule de récurrence de Stahl aux nombres chromatiques . Cette relation s’exprime comme . La conjecture de Bouchet...
A dominating set in a graph is a connected dominating set of if it induces a connected subgraph of . The connected domatic number of is the maximum number of pairwise disjoint, connected dominating sets in . We establish a sharp lower bound on the number of edges in a connected graph with a given order and given connected domatic number. We also show that a planar graph has connected domatic number at most 4 and give a characterization of planar graphs having connected domatic number 3.
The intersection graph of a graph has for vertices all the induced paths of order 3 in . Two vertices in are adjacent if the corresponding paths in are not disjoint. A -container between two different vertices and in a graph is a set of internally vertex disjoint paths between and . The length of a container is the length of the longest path in it. The -wide diameter of is the minimum number such that there is a -container of length at most between any pair of different...
In [1] Burger and Mynhardt introduced the idea of universal fixers. Let G = (V, E) be a graph with n vertices and G’ a copy of G. For a bijective function π: V(G) → V(G’), define the prism πG of G as follows: V(πG) = V(G) ∪ V(G’) and , where . Let γ(G) be the domination number of G. If γ(πG) = γ(G) for any bijective function π, then G is called a universal fixer. In [9] it is conjectured that the only universal fixers are the edgeless graphs K̅ₙ. In this work we generalize the concept of universal...