We show that if, for any fixed \(r\), the neighbourhood unions of all \(r\)-sets of vertices are large enough, then \(G\) will have many edge-disjoint perfect matchings. In particular, we show that given fixed positive integers \(r\) and \(c\) and a graph \(G\) of even order \(n\), if the minimum degree is at least \(r + c – 1\) and if the neighbourhood union of each \(r\)-set of vertices is at least \(n/2 + \left(2\lfloor\frac{(c + 1)}{2}\rfloor – 1\right)r\), then \(G\) has \(c\) edge-disjoint perfect matchings, for \(n\) large enough. This extends earlier work by Faudree, Gould and Lesniak on neighbourhood unions of pairs of vertices.

In this paper, necessary and sufficient conditions for a vector to be the fine structure of a balanced ternary design with block size \(3\), index \(3\) and \(\rho_2 = 1\) and \(2\) are determined, with one unresolved case.

Let \(K^d_n\) be the product of \(d\) copies of the complete graph \(K_4\). Wojciechowski [4] proved that for any \(d \geq 2\) the hypercube \(K^d_2\) can be vertex covered with at most \(16\) disjoint snakes. We show that for any odd integer \(n \geq 3\), \(d \geq 2\) the graph \(K^d_n\) can be vertex covered with \(2n^3\) snakes.

Cwatsets are subsets of \(\mathbb{Z}^d_2\) which are nearly subgroups and which naturally appear in statistics and coding theory [8]. Each cwatset can be represented by a highly symmetric hypergraph [7]. We introduce and study the symmetry group of the hypergraph and connect it to the corresponding cwatset. We use this connection to establish structure theorems for several classes of cwatsets.

Bollobás, Brightwell [1] and independently Shi [3] proved the existence of a cycle through all vertices of degree at least \(\frac{n}{2}\) in any \(2\)-connected graph of order \(n\). The aim of this paper is to show that the above degree requirement can be relaxed for \(1\)-tough graphs.

In this paper we investigate the \(k\)th lower multiexponent \(f(n,k)\) for tournament matrices.
It was proved that \(f(m,3) = 2\) if and only if \(m \geq 11\). Thus the conjecture in [2] is disproved. Further we obtain a new sufficient condition for \(f(n,k) = 1\).

The cycle graph \(C(H)\) of a graph \(H\) is the edge intersection graph of all induced chordless cycles of \(H\). We investigate iterates of the mapping \(\overline{C}: G \rightarrow C(\overline{G})\) where \(C\) denotes the map that associates to a graph its cycle graph. We call a graph \(G\) vanishing under \(\overline{C}\) if \(\overline{C^n}(G) = 0\) for some \(n\), otherwise \(G\) is called \(\overline{C}\)-persistent. We call a graph \(G\) expanding under \(\overline{C}\) if \(|\overline{C^n}(G)| \to \infty\) as \(n \to \infty\). We show that the lowest order of a \(\overline{C}\)-expanding graph is \(6\) and determine the behaviour under \(\overline{C}\) of some special graphs, including trees, null graphs, cycles and complete bipartite graphs.