The bondage number \(b(G)\) of a nonempty graph \(G\) was first introduced by Fink, Jacobson, Kinch, and Roberts [3]. In their paper they conjectured that \(b(G) \leq \Delta(G)+1\) for a nonempty graph \(G\). A counterexample for this conjecture was shown in [5]. Beyond it, we show now that there doesn’t exist an upper bound of the following form: \(b(G) \leq \Delta(G)+c\) for any \(c\in\mathbb{N}\).

It is shown that if \(t > 1\) and \(u \geq 5\), then the known necessary condition for the existence of a skew Room frame of type \(t^u\), is also sufficient with the possible exception of \((u, f)\) where \(u = 5\) and \(t \in \{11, 13, 17, 19, 23, 29, 31, 41, 43\}\).

The class of \(t-sc\) graphs constitutes a new generalization of self-complementary graphs. Many \(t-sc\) graphs exhibit a stable complementing permutation. In this paper, we prove a sufficient condition for the existence of a stable complementing permutation in a \(t-sc\) graph. We also construct several infinite classes of \(t-sc\) graphs to show the stringency of our sufficient condition.

A polyhex graph is either a hexagonal system or a coronoid system. A polyhex graph \(G\) is said to be \(k\)-coverable if for any \(k\) mutually disjoint hexagons the subgraph obtained from \(G\) by deleting all these \(k\) hexagons together with their incident edges has at least one perfect matching. In this paper, a constructive criterion is given to determine whether or not a given polyhex graph is \(k\)-coverable. Furthermore, a simple method is developed which allows us to determine whether or not there exists a \(k\)-coverable polyhex graph with exactly \(h\) hexagons.

A \((k, \lambda)\)-semiframe of type \(g^u\) is a group divisible design of type \(g^u\) \((\chi, \mathcal{G}, \mathcal{B})\), in which \(\mathcal{B}\) is written as a disjoint union \(\mathcal{B} = \mathcal{P} \cup \mathcal{Q} \) where \(\mathcal{P} \) is partitioned into partial parallel classes of \(\chi\) (with respect to some \(G \in \mathcal{G}\)) and \(\mathcal{Q} \) is partitioned into parallel classes of \(\chi\). In this paper, new constructions for these designs are provided with some series of designs with \(k = 3\). Cyclic semiframes are discussed. Finally, an application of semiframes is also mentioned.

A solution of Dudeney’s round table problem is given when \(n\) is as follows:

1. \(n = pq + 1\), where \(p\) and \(q\) are odd primes.
2. \(n = p^e + 1\), where \(p\) is an odd prime.
3. \(n = p^e q^f + 1\), where \(p\) and \(q\) are distinct odd primes satisfying \(p \geq 5\) and \(q \geq 11\), and \(e\) and \(f\) are natural numbers.