The automorphism group of a graph acts on its cocycle space over any field. The orbits of this group action will be counted in case of finite fields. In particular, we obtain an enumeration of non-equivalent edge cuts of the graph.

We give necessary and sufficient conditions on the order of a Steiner triple system admitting an automorphism \(\pi\), consisting of \(1\) large cycle, several cycles of length \(4\) and a fixed point.

A graph \(G = (V, E)\) is said to be elegant if it is possible to label its vertices by an injective mapping \(g\) into \(\{0, 1, \dots, |E|\}\) such that the induced labeling \(h\) on the edges defined for edge \(x, y\) by \(h(x, y) = g(x) + g(y) \mod (|E| + 1)\) takes all the values in \(\{1, \dots, |E|\}\). In the first part of this paper, we prove the existence of a coloring of \(K_n\) with a omnicolored path on \(n\) vertices as subgraph, which had been conjectured by Hastman [2].
In the second part we prove that the cycle on \(n\) vertices is elegant if and only if \(n \neq 1 \pmod{4}\) and we give a new construction of an elegant labeling of the path \(P_n\), where \(n \neq 4\).

A round robin tournament on \(q\) players in which draws are not permitted is said to have property \(P(n, k)\) if each player in any subset of \(n\) players is defeated by at least \(k\) other players. We consider the problem of determining the minimum value \(F(n, k)\) such that every tournament of order \(q \geq F(n, k)\) has property \(P(n, k)\). The case \(k = 1\) has been studied by Erdős, G. and E. Szekeres, Graham and Spencer, and Bollobás. In this paper we present a lower bound on \(F(n, k)\) for the case of Paley tournaments.

Upper and lower bounds are established for the toughness of the generalized Petersen graphs \(G(n,2)\) for \(n \geq 5\), and all non-isomorphic disconnecting sets that achieve the toughness are presented for \(5 \leq n \leq 15\). These results also provide an infinite class of \(G(n,2)\) for which the toughness equals \(\frac{5}{4}\), namely when \(n \equiv 0 (\mod 7)\).

Let \(m\) be a double occurrence word (i.e., each letter occurring in \(m\) occurs precisely twice). An alternance of \(m\) is a non-ordered pair \(uw\) of distinct letters such that we meet alternatively \(\dots v \dots w \dots v \dots w \dots\) when reading \(m\). The alternance graph \(A(m)\) is the simple graph whose vertices are the letters of \(m\) and whose edges are the alternances of \(m\). We define a transformation of double occurrence words such that whenever \(A(m) = A(n)\), \(m\) and \(n\) are related by a sequence of these transformations.

A graph \(G\) is a sum graph if there is a labeling \(o\) of its vertices with distinct positive integers, so that for any two distinct vertices \(u\) and \(v\), \(uv\) is an edge of \(G\) if and only if \(\sigma(u) +\sigma(v) = \sigma(w)\) for some other vertex \(w\). Every sum graph has at least one isolated vertex (the vertex with the largest label). Harary has conjectured that any tree can be made into a sum graph with the addition of a single isolated vertex. We prove this conjecture.

An \(H\)-decomposition of a graph \(G\) is a representation of \(G\) as an edge disjoint union of subgraphs, all of which are isomorphic to another graph \(H\). We study the case where \(H\) is \(P_3 \cup tK_2\) – the vertex disjoint union of a simple path of length 2 (edges) and \(t\) isolated edges – and prove that a set of three obviously necessary conditions for \(G = (V, E)\) to admit an \(H\)-decomposition, is also sufficient if \(|E|\) exceeds a certain function of \(t\). A polynomial time algorithm to test \(H\)-decomposability of an input graph \(G\) immediately follows.

In this paper we consider group divisible designs with equal-sized holes \((HGDD)\) which is a generalization of modified group divisible designs \([1]\) and \(HMOLS\). We prove that the obvious necessary conditions for the existence of the \(HGDD\) is sufficient when the block size is three, which generalizes the result of Assaf[1].