Ground state incongruence in 2D spin glasses revisited.
The prime graph of a finite group is defined as follows: the set of vertices is , the set of primes dividing the order of , and two vertices , are joined by an edge (we write ) if and only if there exists an element in of order . We study the groups such that the prime graph is a tree, proving that, in this case, .
The Grundy number of a graph G is the maximum number k of colors used to color the vertices of G such that the coloring is proper and every vertex x colored with color i, 1 ≤ i ≤ k, is adjacent to (i-1) vertices colored with each color j, 1 ≤ j ≤ i -1. In this paper we give bounds for the Grundy number of some graphs and cartesian products of graphs. In particular, we determine an exact value of this parameter for n-dimensional meshes and some n-dimensional toroidal meshes. Finally, we present an...
For two vertices and in a connected graph , the set consists of all those vertices lying on a geodesic in . For a set of vertices of , the union of all sets for is denoted by . A set is convex if . The convexity number is the maximum cardinality of a proper convex set in . A convex set is maximum if . The cardinality of a maximum convex set in a graph is the convexity number of . For a nontrivial connected graph , a connected graph is an -convex graph if contains...