A list version of graph packing

We consider the following generalization of graph packing. Let $G_{1} = (V_{1}, E_{1})$ and $G_{2} = (V_{2}, E_{2})$ be graphs of order $n$ and $G_{3} = (V_{1} \cup V_{2}, E_{3})$ a bipartite graph. A bijection $f$ from $V_{1}$ onto $V_{2}$ is a list packing of the triple $(G_{1}, G_{2}, G_{3})$ if $uv \in E_{2}$ implies $f(u)f(v) \notin E_{2}$ and $vf(v) \notin E_{3}$ for all $v \in V_{1}$. We extend the classical results of Sauer and Spencer and Bollob\'{a}s and Eldridge on packing of graphs with small sizes or maximum degrees to the setting of list packing. In particular, we extend the well-known Bollob\'{a}s--Eldridge Theorem, proving that if $\Delta (G_{1}) \leq n-2, \Delta(G_{2}) \leq n-2, \Delta(G_{3}) \leq n-1$, and $|E_1| + |E_2| + |E_3| \leq 2n-3$, then either $(G_{1}, G_{2}, G_{3})$ packs or is one of 7 possible exceptions. Hopefully, the concept of list packing will help to solve some problems on ordinary graph packing, as the concept of list coloring did for ordinary coloring.Comment: 10 pages, 4 figure

The Tur\'an number of sparse spanning graphs

For a graph $H$, the {\em extremal number} $ex(n,H)$ is the maximum number of edges in a graph of order $n$ not containing a subgraph isomorphic to $H$. Let $\delta(H)>0$ and $\Delta(H)$ denote the minimum degree and maximum degree of $H$, respectively. We prove that for all $n$ sufficiently large, if $H$ is any graph of order $n$ with $\Delta(H) \le \sqrt{n}/200$, then $ex(n,H)={{n-1} \choose 2}+\delta(H)-1$. The condition on the maximum degree is tight up to a constant factor. This generalizes a classical result of Ore for the case $H=C_n$, and resolves, in a strong form, a conjecture of Glebov, Person, and Weps for the case of graphs. A counter-example to their more general conjecture concerning the extremal number of bounded degree spanning hypergraphs is also given

On the bipartite graph packing problem

The graph packing problem is a well-known area in graph theory. We consider a bipartite version and give almost tight conditions on the packability of two bipartite sequences

Embedding graphs having Ore-degree at most five

Let $H$ and $G$ be graphs on $n$ vertices, where $n$ is sufficiently large. We prove that if $H$ has Ore-degree at most 5 and $G$ has minimum degree at least $2n/3$ then $H\subset G.$Comment: accepted for publication at SIAM J. Disc. Mat

Graph packing with constraints on edges

A graph consists of a set of vertices (nodes) and a set of edges (line connecting vertices). Two graphs pack when they have the same number of vertices and we can put them in the same vertex set without overlapping edges. Studies such as Sauer and Spencer, Bollobas and Eldridge, Kostochka and Yu, have shown sufficient conditions, specifically relations between number of edges in the two graphs, for two graphs to pack, but only a few addressed packing with constraints. Kostochka and Yu proved that if e_1e_2 \u3c (1 - \eps)n^2, then $G_1$ and $G_2$ pack with exceptions. We extend this finding by using the language of list packing introduced by Gyori, Kostochka, McConvey, and Yager, and we show that the triple $(G_1, G_2, G_3)$ with e_1e_2 + \frac{n-1}{2}\cdot e_3 \u3c (2 - \eps)\binom{n}{2} pack with well-defined exceptions