For a commutative semigroup S with 0, the zero-divisor graph of S denoted by Γ(S) is the graph whose vertices are nonzero zero-divisor of S, and two vertices x, y are adjacent in case xy = 0 in S. In this paper we study the case where the graph Γ(S) is complete r-partite for a positive integer r. Also we study the commutative semigroups which are finitely colorable.

The tree partition number of an r-edge-colored graph G, denoted by tr(G), is the minimum number k such that whenever the edges of G are colored with r colors, the vertices of G can be covered by at most k vertex-disjoint monochromatic trees. We determine t2(K(n1, n2, . . . , nk)) of the complete k-partite graph K(n1, n2, . . . , nk). In particular, we prove that t2(K(n,m)) = (m − 2)/2n + 2, whe...

We find unitary matrix solutions˜R(a) to the (multiplicative parameter-dependent) (N, z)-generalized Yang-Baxter equation that carry the standard measurement basis to m-level N-partite entangled states that generalize the 2-level bipartite entangled Bell states. This is achieved by a careful study of solutions to the Yang-Baxter equation discovered by Fateev and Zamolodchikov in 1982.

We study a game on a graph G played by r revolutionaries and s spies. Initially, revolutionaries and then spies occupy vertices. In each subsequent round, each revolutionary may move to a neighboring vertex or not move, and then each spy has the same option. The revolutionaries win if m of them meet at some vertex having no spy (at the end of a round); the spies win if they can avoid this forev...

Given a coloring of the edges of a multi-hypergraph, a rainbow t-matching is a collection of t disjoint edges, each having a different color. In this note we study the problem of finding a rainbow t-matching in an r-partite r-uniform multi-hypergraph whose edges are colored with f colors such that every color class is a matching of size t. This problem was posed by Aharoni and Berger, who asked...

Abstract. Two central topics of study in combinatorics are the so-called evolution of random graphs, introduced by the seminal work of Erdős and Rényi, and the family of H-free graphs, that is, graphs which do not contain a subgraph isomorphic to a given (usually small) graph H . A widely studied problem that lies at the interface of these two areas is that of determining how the structure of a...

We extend results on monochromatic tree covers and from classical Ramsey theory to a generalised setting, where each of the edges of an underlying host graph (here, either a complete graph or a complete bipartite graph), is coloured with a set of colours. Our results for tree covers in this setting have an application to Ryser’s Conjecture. Every r-partite r-uniform hypergraph whose edges pairw...

We investigate the threshold probability for the property that every r-coloring of the edges of a random binomial k-uniform hypergraph G(k)(n, p) yields a monochromatic copy of some fixed hypergraph G. In this paper we solve the problem for arbitrary k ≥ 3 and k-partite, k-uniform hypergraphs G.

We address the following problem: Given a complete k-partite geometric graph K whose vertex set is a set of n points in R, compute a spanner of K that has a “small” stretch factor and “few” edges. We present two algorithms for this problem. The first algorithm computes a (5 + )-spanner of K with O(n) edges in O(n log n) time. The second algorithm computes a (3 + )-spanner of K with O(n log n) e...