A finite group is called \(P_n\)-sequenceable if its nonidentity elements can be listed \(x_1, x_2, \ldots, x_{k}\) such that the product \(x_i x_{i+1} \cdots x_{i+n-1}\) can be rewritten in at least one nontrivial way for all \(i\). It is shown that \(S_n, A_n, D_n\) are \(P_3\)-sequenceable, that every finite simple group is \(P_4\)-sequenceable, and that every finite group is \(P_5\)-sequenceable. It is conjectured that every finite group is \(P_3\)-sequenceable.

In this paper, we give two constructive proofs that all \(4\)-stars are Skolem-graceful. A \(4\)-star is a graph with 4 components, with at most one vertex of degree exceeding 1 per component. A graph \(G = (V, E)\) is Skolem-graceful if its vertices can be labelled \(1, 2, \ldots, |V|\) so that the edges are labelled \(1, 2, \ldots, |E|\), where each edge-label is the absolute difference of the labels of the two end-vertices. Skolem-gracefulness is related to the classic concept of gracefulness, and the methods we develop here may be useful there.

We consider two seemingly related problems. The first concerns pairs of graphs \(G\) and \(H\) containing endvertices (vertices of degree \(1\)) and having the property that, although they are not isomorphic, they have the same collection of endvertex-deleted subgraphs.

The second question concerns graphs \(G\) containing endvertices and having the property that, although no two endvertices are similar, any two endvertex-deleted subgraphs of \(G\) are isomorphic.

A graph \(G\) is supereulerian if it contains a spanning eulerian subgraph. Let \(n\), \(m\), and \(p\) be natural numbers, \(m, p \geq 2\). Let \(G\) be a \(2\)-edge-connected simple graph on \(n > p + 6\) vertices containing no \(K_{m+1}\). We prove that if

\[|E(G)\leq \binom{n-p+1-k}{2}+(m-1)\binom{k+1}{2}+2p-4, \quad (1)]\

where \(k = \lfloor\frac{n-p+1}{m}\rfloor\), then either \(G\) is supereulerian, or \(G\) can be contracted to a non-supereulerian graph of order less than \(p\), or equality holds in (1) and \(G\) can be contracted to \(K_{2,p-2}\) (p is odd) by contracting a complete \(m\)-partite graph \(T_{m,n-p+1}\) of order \(n – p + 1\) in \(G\). This is a generalization of the previous results in [3] and [5].

Steiner triple systems admitting automorphisms whose disjoint cyclic decomposition consist of two cycles are explored. We call such systems bicyclic . Several necessary conditions are given. Sufficient conditions are given when the length of the smaller cycle is \(7\).

The \(\Delta\)-subgraph \(G_\Delta \) of a simple graph \(G\) is the subgraph induced by the vertices of maximum degree of \(G\). In this paper, we obtain some results about the construction of a graph \(G\) if the graph \(G\) is Class 2 and the structure of \(G_\Delta \) is particularly simple.

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.