A set S ⊆ V is a global dominating set of a graph G = (V,E) if S is a dominating set of G and G, where G is the complement graph of G. The global domination number γg(G) equals the minimum cardinality of a global dominating set of G. The square graph G of a graph G is the graph with vertex set V and two vertices are adjacent in G if they are joined in G by a path of length one or two. In this p...

For an integer k ≥ 1 and a graph G = (V,E), a subset S of V is kindependent if every vertex in S has at most k − 1 neighbors in S. The k-independent number βk(G) is the maximum cardinality of a kindependent set of G. In this work, we study relations between βk(G), βj(G) and the domination number γ(G) in a graph G where 1 ≤ j < k. Also we give some characterizations of extremal graphs.

A total dominating set of a graph G is a set S of vertices of G such that every vertex is adjacent to a vertex in S. The total domination number of G, denoted by γt(G), is the minimum cardinality of a total dominating set. Let G be a connected spanning subgraph of Ks,s and letH be the complement of G relative to Ks,s; that is, Ks,s = G⊕H . The graph G is k-supercritical relative to Ks,s if γt(G...

In this paper, we study the minimality of the boundary of a Coxeter system. We show that for a Coxeter system (W,S) if there exist a maximal spherical subset T of S and an element s0 ∈ S such that m(s0, t) ≥ 3 for each t ∈ T and m(s0, t0) = ∞ for some t0 ∈ T , then every orbit Wα is dense in the boundary ∂Σ(W,S) of the Coxeter system (W,S), hence ∂Σ(W,S) is minimal, where m(s0, t) is the order ...

We investigate the parameterized complexity of Maximum Independent Set and Dominating Set restricted to certain geometric graphs. We show that Dominating Set is W[1]-hard for the intersection graphs of unit squares, unit disks, and line segments. For Maximum Independent Set, we show that the problem is W[1]-complete for unit segments, but fixed-parameter tractable if the segments are axis-paral...

A set of vertices of a graph G is a total dominating set if each vertex of G is adjacent to a vertex in the set. The total domination number of a graph γt (G) is the minimum size of a total dominating set. We provide a short proof of the result that γt (G) ≤ 2 3 n for connected graphs with n ≥ 3 and a short characterization of the extremal graphs.

A set S V is a dominating set of a graph G = (V;E) if each vertex in V is either in S or is adjacent to a vertex in S. A vertex is said to dominate itself and all its neighbors. The domination number (G) is the minimum cardinality of a dominating set of G. In terms of a chess board problem, let Xn be the graph for chess pieceX on the square of side n. Thus, (Xn) is the domination number for che...

Recently, the authors studied the connection between each maximal monotone operator T and a family H(T ) of convex functions. Each member of this family characterizes the operator and satisfies two particular inequalities. The aim of this paper is to establish the converse of the latter fact. Namely, that every convex function satisfying those two particular inequalities is associated to a uniq...

We are concerned with the poset P(n)=P([1, 2, ..., n]). This is the power set of [n]=[1, 2, ..., n], ordered by inclusion. A set system is simply a subset of P(n). A set system is an antichain if no two of its members are comparable. Conversely a chain is a totally ordered set system. We shall often consider maximal chains; those chains which cannot be extended. In particular such chains contai...

A point in the plane is called a guard for the convex set C if it lies in the interior of C. Let P be a planar point-set. A set S of points is a k-convex guard set for P if every convex k-gon formed from points of P contains a guard from S. We study, for any integer k 3, the minimum size of a k-convex guard set of a given planar point-set of size n. We give the tight bounds for the case k = 3, ...