Let G be a simple connected graph. The distinguishing number of G, denoted by D(G), is the least integer d such that G has a vertex d-labeling preserved only by the trivial automorphism. In this paper, we characterize all graphs of order n with distinguishing number n − 1, or n − 2.

We study the problem of reconstruction of a simplicial 2-complex from its 1- skeleton together with the prescribed quantities of 2-simplices at each 1-simplex, under the restriction that these quantities are bounded above by 2. It is a known fact that a 2-complex is uniquely reconstructible, or “combinatorially rigid”, if it has 5 or fewer vertices. In this paper “combinatorially flexible” 2-complexes (that is, non-uniquely reconstructible from their 1-skeletons) with 6 vertices are characterized in terms of necessary 2-subcomplexes.

The weakened Ramsey number $r^{s,t}(G)$ is defined to be the least $p\in \mathbb{N}$ such that every $t$-coloring of the edges of the complete graph $K_p$ contains a subgraph isomorphic to $G$ that is spanned by edges that use at most $s$ colors ($1\le s\le t-1$). The star-critical weakened Ramsey number $r^{s,t}_*(G)$ then determines the minimum number of edges that must join a vertex to $K_{r^{s,t}(G)-1}$ in order for this Ramsey property to hold. We begin by showing that $r_*^{s,t}(K_n)=r^{s,t}(K_n)-1$ for all $n\in \mathbb{N}$. Then, building off of Khamseh and Omidi's recent determination of $r^{s,t}(K_{1,n})$ when $s=t-1$ and $s=t-2$, we focus on the evaluation of $r_*^{t-1,t}(K_{1,n})$ and $r_*^{t-2,t}(K_{1,n})$. Additionally, we determine $r^{2,t}(K_{1,3})$ and $r_*^{2,t}(K_{1,3})$ when $t\ge 3$.

For a family $\mathcal{H}$ of graphs, a graph $G$ is said to be $\mathcal{H}$-free if $G$ contains no member of $\mathcal{H}$ as an induced subgraph. Let $\mathcal{G}_2^{(3)}}(\mathcal{H})$ denote the family of $2$-connected $\mathcal{H}$-free graphs having minimum degree at least $3$. This paper is concerned with families $\mathcal{H}$ of connected graphs with $|\mathcal{H}| = 3$ such that $\mathcal{G}_2^{(3)}}(\mathcal{H})$ is a finite family. In particular, we show that for a connected graph $T$ of order at least $3$ that is not a star, $\mathcal{G}_2^{(3)}(\{K_4,K_{2,2},T\})$ is finite if and only if $T$ is a path of order at most $6$.

It is conjectured that the mxn grid graph has a prime labeling for all positive integers m and n. It is known that for any prime p and any integer n such that 1≤n≤p2, there exists a prime labeling on the pxn grid graph Pm x Pn. Also, it is known that the ladder P2 x Pn has a prime labeling for all positive integers n. We assume that Goldbach's Even Conjecture and a strengthened variant of Lemoine's Conjecture are true in order to show that the 3xn grid graph P3 x Pn has a prime labeling for every positive integer n. As a result, P3 x Pn has a prime labeling for every positive integer n≤107.