## Abstract Hall's condition is a simple requirement that a graph __G__ and list assignment __L__ must satisfy if __G__ is to have a proper __L__‐colouring. The Hall number of __G__ is the smallest integer __m__ such that whenever the lists on the vertices each has size at least __m__ and Hall's co
Characterization of the graphs with boxicity ⩽2
✍ Scribed by Martin Quest; Gerd Wegner
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 360 KB
- Volume
- 81
- Category
- Article
- ISSN
- 0012-365X
No coin nor oath required. For personal study only.
✦ Synopsis
The intersection graph of a family 8TI of sets has the sets in %' as vertices and an edge between two sets iff they have nonempty intersection. Following Roberts [4] the boxicity b(G) of a graph G is defined as the smallest d such that G is the intersection graph of boxes in Euclidean d-space, i.e. parallelepipeds with edges parallel to the coordinate axes. In this paper we will give a combinatorial characterization of the graphs with b(G)s2, called boxicity 2-graphs, by means of the arrangement of zeros and ones in special matrices attached to the graph.
📜 SIMILAR VOLUMES
We prove that or,@) s 6k, for L~-coioured graphs. Let G = (V, S) be an undirected graph. For every pair of distinct elements X, y E V, the &stcPnce d(x, y) is the length of a shortest path joining them if one exists, otherwise d(x, y) = 00. In the case x = y, it is d(x, y) = 0. If 6; = (V, S) is a
A graph G is called a D-graph if for every set of cliques of G whose pairwise intersections are nonempty there is a vertex of G common to all the cliques of the set. A D-graph G is called a Dl-graph if it has the T 1 property: for any two distinct vertices x and y of G, there exist cliques C and D o
## Abstract A graph __G__ is critically 2‐connected if __G__ is 2‐connected but, for any point __p__ of __G, G — p__ is not 2‐connected. Critically 2‐connected graphs on __n__ points that have the maximum number of lines are characterized and shown to be unique for __n__ ⩾ 3, __n__ ≠ 11.
A graph is said to be k-variegated if its vertex set can be partiticned into k equal parts such that each vertex is adjacent to exactly one vertex from every othe,r part not co;ltaininT, it. We prove that a graph G on 2n vertices is 2-variegated if and only if there exists a bet S of n independent e