The maximality of the Suzuki group \(\text{Sz}(K,a)\), \(K\) any commutative field of characteristic \(2\) admitting an automorphism \(\sigma\) such that \(x^{\sigma^2} = x^2\), in the symplectic group \(\text{PSp}_4(K)\), is proved.

Let \(k\) be a positive integer and \(G = (V, E)\) be a connected graph of order \(n\). A set \(D \subseteq V\) is called a \(k\)-dominating set of \(G\) if each \(x \in V(G) – D\) is within distance \(k\) from some vertex of \(D\). A connected \(k\)-dominating set is a \(k\)-dominating set that induces a connected subgraph of \(G\). The connected \(k\)-domination number of \(G\), denoted by \(\gamma_k^c(G)\), is the minimum cardinality of a connected \(k\)-dominating set. Let \(\delta\) and \(\Delta\) denote the minimum and the maximum degree of \(G\), respectively. This paper establishes that \(\gamma_k^c(G) \leq \max\{1, n – 2k – \Delta + 2\}\), and \(\gamma_k^c(G) \leq (1 + o_\delta(1))n \frac{ln[m(\delta+1)+2-t]}{m(\delta+1)+2-t}\), where \(m = \lceil \frac{k}{3} \rceil\), \(t = 3 \lceil \frac{k}{3} \rceil – k\), and \(o_\delta(1)\) denotes a function that tends to \(0\) as \(\delta \to \infty\). The later generalizes the result of Caro et al. in [Connected domination and spanning trees with many leaves. SIAM J. Discrete Math. 13 (2000), 202-211] for \(k = 1\).

A graph \(U\) is (induced)-universal for a class of graphs \({X}\) if every member of \({X}\) is contained in \(U\) as an induced subgraph. We study the problem of finding universal graphs with minimum number of vertices for various classes of bipartite graphs: exponential classes, bipartite chain graphs, bipartite permutation graphs, and general bipartite graphs. For exponential classes and general bipartite graphs we present a construction which is asymptotically optimal, while for the other classes our solutions are optimal in order.

The multicolor Ramsey number \(R_r(H)\) is defined to be the smallest integer \(n = n(r)\) with the property that any \(r\)-coloring of the edges of complete graph \(K_n\) must result in a monochromatic subgraph of \(K_n\) isomorphic to \(H\). In this paper, we study the case that \(H\) is a cycle of length \(2k\). If \(2k \geq r+1\) and \(r\) is a prime power, we show that \(R_r(C_{2k}) > {r^2+2k-r-1}\).

The bondage number \(b(D)\) of a digraph \(D\) is the cardinality of a smallest set of arcs whose removal from \(D\) results in a digraph with domination number greater than the domination number of \(D\). In this paper, we present some upper bounds on bondage number for oriented graphs including tournaments, and symmetric planar digraphs.

Let \(G\) be a connected graph. For a vertex \(v \in V(G)\) and an ordered \(k\)-partition \(\Pi = \{S_1, S_2, \ldots, S_k\}\) of \(V(G)\), the representation of \(v\) with respect to \(\Pi\) is the \(k\)-vector \(r(v|\Pi) = (d(v, S_1), d(v, S_2), \ldots, d(v, S_k))\). The \(k\)-partition \(\Pi\) is said to be resolving if the \(k\)-vectors \(r(v|\Pi), v \in V(G)\), are distinct. The minimum \(k\) for which there is a resolving \(k\)-partition of \(V(G)\) is called the partition dimension of \(G\), denoted by \(pd(G)\). A resolving \(k\)-partition \(\Pi = \{S_1, S_2, \ldots, S_k\}\) of \(V(G)\) is said to be connected if each subgraph \(\langle S_i \rangle\) induced by \(S_i\) (\(1 \leq i \leq k\)) is connected in \(G\). The minimum \(k\) for which there is a connected resolving \(k\)-partition of \(V(G)\) is called the connected partition dimension of \(G\), denoted by \(cpd(G)\). In this paper, the partition dimension as well as the connected partition dimension of the wheel \(W_n\) with \(n\) spokes are considered, by showing that \(\lceil (2n)^{1/3} \rceil \leq pd(W_n) \leq \lceil 2(n)^{1/2} \rceil +1\) and \(cpd(W_n) = \lceil (n+2)/3 \rceil\) for \(n \geq 4\).

Vertices \(x\) and \(y\) are called paired in tournament \(T\) if there exists a vertex \(z\) in the vertex set of \(T\) such that either \(x\) and \(y\) beat \(z\) or \(z\) beats \(x\) and \(y\). Vertices \(x\) and \(y\) are said to be distinguished in \(T\) if there exists a vertex \(z\) in \(T\) such that either \(x\) beats \(z\) and \(z\) beats \(y\), or \(y\) beats \(z\) and \(z\) beats \(x\). Two vertices are strictly paired (distinguished) in \(T\) if all vertices of \(T\) pair (distinguish) the two vertices in question. The \(p/d\)-graph of a tournament \(T\) is a graph which depicts strictly paired or strictly distinguished pairs of vertices in \(T\). \(P/d\)-graphs are useful in obtaining the characterization of such graphs as domination and domination-compliance graphs of tournaments. We shall see that \(p/d\)-graphs of tournaments have an interestingly limited structure as we characterize them in this paper. In so doing, we find a method of constructing a tournament with a given \(p/d\)-graph using adjacency matrices of tournaments.

Let \(G\) be a simple connected graph. The spectral radius \(\rho(G)\) of \(G\) is the largest eigenvalue of its adjacency matrix. In this paper, we obtain two lower bounds of \(\rho(G)\) by two different methods, one of which is better than another in some conditions.

In this note we compute the chromatic polynomial of the Jahangir graph \(J_{2p}\) and we prove that it is chromatically unique for \(p=3\).

In this paper, we compute the PI and Szeged indices of some important classes of benzenoid graphs, which some of them are related to nanostructures. Some open questions are also included.