The 1, 2, 3-Conjecture states that the edges of a graph without isolated edges can be labeled from {1, 2, 3} so that the sums of labels at adjacent vertices are distinct. The 1, 2-Conjecture states that if vertices also receive labels and the vertex label is added to the sum of its incident edge labels, then adjacent vertices can be distinguished using only {1, 2}. We show that various configurations cannot occur in minimal counterexamples to these conjectures. Discharging then confirms the conjectures...

An edge ordering of a graph G is an injection f : E(G) → R, the set of real numbers. A path in G for which the edge ordering f increases along its edge sequence is called an f-ascent ; an f-ascent is maximal if it is not contained in a longer f-ascent. The depression of G is the smallest integer k such that any edge ordering f has a maximal f-ascent of length at most k. A k-kernel of a graph G is a set of vertices U ⊆ V (G) such that for any edge ordering f of G there exists a maximal f-ascent of...

If $G$ is a connected graph of order $n\ge 1$, then by a hamiltonian coloring of $G$ we mean a mapping $c$ of $V\left(G\right)$ into the set of all positive integers such that $|c\left(x\right)-c\left(y\right)|\ge n-1-D_G(x,y)$ (where $D_G(x,y)$ denotes the length of a longest $x-y$ path in $G$) for all distinct $x,y\in V\left(G\right)$. Let $G$ be a connected graph. By the hamiltonian chromatic number of $G$ we mean $$min(max(c\left(z\right);z\in V\left(G\right)\left)\right),$$ where the minimum is taken over all hamiltonian colorings $c$ of $G$. The main result of this paper can be formulated as follows: Let $G$ be a connected graph of order $n\ge 3$. Assume that there exists a subgraph...

For a nontrivial connected graph $G$ of order $n$, the detour distance $D(u,v)$ between two vertices $u$ and $v$ in $G$ is the length of a longest $u-v$ path in $G$. Detour distance is a metric on the vertex set of $G$. For each integer $k$ with $1\le k\le n-1$, a coloring $c:V\left(G\right)\to \mathbb{N}$ is a $k$-metric coloring of $G$ if $\left|c\right(u)-c(v\left)\right|+D(u,v)\ge k+1$ for every two distinct vertices $u$ and $v$ of $G$. The value ${\chi }_m^k\left(c\right)$ of a $k$-metric coloring $c$ is the maximum color assigned by $c$ to a vertex of $G$ and the $k$-metric chromatic number ${\chi }_m^k\left(G\right)$ of $G$ is the minimum value of a $k$-metric coloring of $G$. For every...

Suppose that G is a simple, vertex-labeled graph and that S is a multiset. Then if there exists a one-to-one mapping between the elements of S and the vertices of G, such that edges in G exist if and only if the absolute difference of the corresponding vertex labels exist in S, then G is an autograph, and S is a signature for G. While it is known that many common families of graphs are autographs, and that infinitely many graphs are not autographs, a non-autograph has never been exhibited. In this...

A d-uniform hypergraph is a sum hypergraph iff there is a finite S ⊆ IN⁺ such that is isomorphic to the hypergraph ${⁺}_d\left(S\right)=(V,)$, where V = S and $=v₁,...,v_d:\left(i\ne j\Rightarrow v_i\ne v_j\right)\wedge {\sum }_{i=1}^d{v}_i\in S$. For an arbitrary d-uniform hypergraph the sum number σ = σ() is defined to be the minimum number of isolated vertices $w₁,...,w_{\sigma }\notin V$ such that $\cup w₁,...,w_{\sigma }$ is a sum hypergraph. In this paper, we prove $\sigma {(}_{n₁,...,n_d}^d)=1+{\sum }_{i=1}^d(n_i-1)+min0,\lceil 1/2({\sum }_{i=1}^{d-1}(n_i-1)-n_d)\rceil$, where ${}_{n₁,...,n_d}^d$ denotes the d-partite complete hypergraph; this generalizes the corresponding result of Hartsfield and Smyth [8] for complete bipartite graphs.

The focus of this article is on three of the author's open conjectures. The article itself surveys results relating to the conjectures and shows where the conjectures are known to hold.

A total edge-irregular k-labelling ξ:V(G)∪ E(G) → {1,2,...,k} of a graph G is a labelling of vertices and edges of G in such a way that for any different edges e and f their weights wt(e) and wt(f) are distinct. The weight wt(e) of an edge e = xy is the sum of the labels of vertices x and y and the label of the edge e. The minimum k for which a graph G has a total edge-irregular k-labelling is called the total edge irregularity strength of G, tes(G). In this paper we prove that for every...

A total vertex irregular k-labeling φ of a graph G is a labeling of the vertices and edges of G with labels from the set {1,2,...,k} in such a way that for any two different vertices x and y their weights wt(x) and wt(y) are distinct. Here, the weight of a vertex x in G is the sum of the label of x and the labels of all edges incident with the vertex x. The minimum k for which the graph G has a vertex irregular total k-labeling is called the total vertex irregularity strength of G. We have determined...

We examine constructions of non-symmetric trees with a flexible q-labeling or an α-like labeling, which allow factorization of $K_{2n}$ into spanning trees, arising from the trees with α-labelings.