On the absolute sum of chromatic polynomial coefficient of graphs.
On the Boolean function graph of a graph and on its complement
For any graph , let and denote the vertex set and the edge set of respectively. The Boolean function graph of is a graph with vertex set and two vertices in are adjacent if and only if they correspond to two adjacent vertices of , two adjacent edges of or to a vertex and an edge not incident to it in . For brevity, this graph is denoted by . In this paper, structural properties of and its complement including traversability and eccentricity properties are studied. In addition,...
On the chromatic number of intersection graphs of convex sets in the plane.
On the chromatic number of rational five-space.
On the chromatic number of simple triangle-free triple systems.
On the chromatic uniqueness of edge-gluing of complete tripartite graphs and cycles.
On the cost chromatic number of outerplanar, planar, and line graphs
We consider vertex colorings of graphs in which each color has an associated cost which is incurred each time the color is assigned to a vertex. The cost of the coloring is the sum of the costs incurred at each vertex. The cost chromatic number of a graph with respect to a cost set is the minimum number of colors necessary to produce a minimum cost coloring of the graph. We show that the cost chromatic number of maximal outerplanar and maximal planar graphs can be arbitrarily large and construct...
On the defining number for vertex colorings of a family of graphs.
On the degrees of graphs with
On the dichromatic number in kernel theory
On the dominator colorings in trees
In a graph G, a vertex is said to dominate itself and all its neighbors. A dominating set of a graph G is a subset of vertices that dominates every vertex of G. The domination number γ(G) is the minimum cardinality of a dominating set of G. A proper coloring of a graph G is a function from the set of vertices of the graph to a set of colors such that any two adjacent vertices have different colors. A dominator coloring of a graph G is a proper coloring such that every vertex of V dominates all vertices...
On the edge coloring of graph products.
On the factorization of reducible properties of graphs into irreducible factors
A hereditary property R of graphs is said to be reducible if there exist hereditary properties P₁,P₂ such that G ∈ R if and only if the set of vertices of G can be partitioned into V(G) = V₁∪V₂ so that ⟨V₁⟩ ∈ P₁ and ⟨V₂⟩ ∈ P₂. The problem of the factorization of reducible properties into irreducible factors is investigated.
On the genus of the complex projective plane.
On the Graph of Large Distances.
On the heterochromatic number of circulant digraphs
The heterochromatic number hc(D) of a digraph D, is the minimum integer k such that for every partition of V(D) into k classes, there is a cyclic triangle whose three vertices belong to different classes. For any two integers s and n with 1 ≤ s ≤ n, let be the oriented graph such that is the set of integers mod 2n+1 and In this paper we prove that for n ≥ 7. The bound is tight since equality holds when s ∈ n,[(2n+1)/3].
On the Independence Number of Edge Chromatic Critical Graphs
In 1968, Vizing conjectured that for any edge chromatic critical graph G = (V,E) with maximum degree △ and independence number α (G), α (G) ≤ [...] . It is known that α (G) < [...] |V |. In this paper we improve this bound when △≥ 4. Our precise result depends on the number n2 of 2-vertices in G, but in particular we prove that α (G) ≤ [...] |V | when △ ≥ 5 and n2 ≤ 2(△− 1)
On the lower bound for the chromatic number of graphs with given maximal degree and girth.
On the maximum average degree and the incidence chromatic number of a graph.
On the number of Russell’s socks or
The following question is analyzed under the assumption that the Axiom of Choice fails badly: Given a countable number of pairs of socks, then how many socks are there? Surprisingly this number is not uniquely determined by the above information, thus giving rise to the concept of Russell-cardinals. It will be shown that: • some Russell-cardinals are even, but others fail to be so; • no Russell-cardinal is odd; • no Russell-cardinal is comparable with any cardinal of the form or ; • finite sums...