Chen, Lih, and Wu conjectured that for r≥3, the only connected graphs with maximum degree at most r that are not equitably r-colorable are Kr,r (for odd r) and Kr+1. If true, this would be a strengthening of the Hajnal–Szemerédi Theorem and Brooks’ Theorem. We extend their conjecture to disconnected graphs. For r≥6 the conjecture says the following: If an r-colorable graph G with maximum degree...

Let G be graph and let S be a set of lists of colon; at the vertices G is said to be S list-colorable if there exists a proper' /'rllnr"'Hl of G sllch that each vertexi takes its color . Alan and Tarsi! I] have shown that G is S list-colorable if and only if its graph polynomial fC(;1;..):= IT(Xi Xj) i~J does not lie in the ideal I generated by the annihilator polynomials colors available at th...

There are many hard conjectures in graph theory, like Tutte’s 5-flow conjecture, and the 5-cycle double cover conjecture, which would be true in general if they would be true for cubic graphs. Since most of them are trivially true for 3-edge-colorable cubic graphs, cubic graphs which are not 3-edge-colorable, often called snarks, play a key role in this context. Here, we survey parameters measu...

For graphs of bounded maximum average degree, we consider the problem of 2-distance coloring. This is the problem of coloring the vertices while ensuring that two vertices that are adjacent or have a common neighbor receive different colors. It is already known that planar graphs of girth at least 6 and of maximum degree∆ are list 2-distance (∆ + 2)-colorable when ∆ ≥ 24 (Borodin and Ivanova (2...

A subgraph H of a multigraph G is called strongly spanning, if any vertex of G is not isolated in H , while it is called maximum k-edge-colorable, if H is proper k-edge-colorable and has the largest size. We introduce a graph-parameter sp(G), that coincides with the smallest k that a graph G has a strongly spanning maximum k-edge-colorable subgraph. Our first result offers some alternative defi...

A cubic graph G is S-edge-colorable for a Steiner triple system S if its edges can be colored with points of S in such a way that the points assigned to three edges Electronic Notes in Discrete Mathematics 29 (2007) 23–27 1571-0653/$ – see front matter © 2007 Elsevier B.V. All rights reserved. www.elsevier.com/locate/endm doi:10.1016/j.endm.2007.07.005 sharing a vertex form a triple in S. We sh...

A subgraph H of a multigraph G is called strongly spanning, if any vertex of G is not isolated in H. H is called maximum k-edge-colorable, if H is proper k-edge-colorable and has the largest size. We introduce a graph-parameter sp(G), that coincides with the smallest k for which a multigraph G has a maximum k-edge-colorable subgraph that is strongly spanning. Our first result offers some altern...

A graph G = (V ,E) is list L-colorable if for a given list assignment L = {L(v) : v ∈ V }, there exists a proper coloring c of G such that c(v) ∈ L(v) for all v ∈ V . If G is list L-colorable for every list assignment with |L(v)| k for all v ∈ V , then G is said to be k-choosable. In this paper, we prove that (1) every planar graph either without 4and 5-cycles, and without triangles at distance...

An even 2-factor is one such that each cycle of length. A 4- regular graph G 4-edge-colorable if and only has two edge-disjoint 2- factors whose union contains all edges in G. It known the line a cubic without 3-edge-coloring not 4-edge-colorable. Hence, we are interested whether those graphs have an 2-factor. Bonisoli Bonvicini proved connected with number 2-factor, perfect matching [Even cycl...

Steinberg asked whether every planar graph without 4 and 5 cycles is 3-colorable. Borodin, and independently Sanders and Zhao, showed that every planar graph without any cycle of length between 4 and 9 is 3-colorable. We improve this result by showing that every planar graph without any cycle of length 4, 5, 6, or 9 is 3-choosable. © 2005 Elsevier B.V. All rights reserved.