Acyclic 4-choosability of planar graphs with neither 4-cycles nor triangular 6-cycles

Every planar graph is known to be acyclically 7-choosable and is conjectured to be acyclically 5-choosable (Borodin et al. 2002) [7]. This conjecture if proved would imply both Borodin’s acyclic 5-color theorem (1979) and Thomassen’s 5-choosability theorem (1994). However, as yet it has been verified only for several restricted classes of graphs.Some sufficient conditions are also obtained for a planar graph to be acyclically 4-choosable and 3-choosable. In particular, acyclic 4-choosability was proved for the following planar graphs: without 3-cycles and 4-cycles (Montassier, 2006 [23]), without 4-cycles, 5-cycles and 6-cycles (Montassier et al. 2006 [24]), and either without 4-cycles, 6-cycles and 7-cycles, or without 4-cycles, 6-cycles and 8-cycles (Chen et al. 2009 [14]).In this paper it is proved that each planar graph with neither 4-cycles nor 6-cycles adjacent to a triangle is acyclically 4-choosable, which covers these four results.     

Acyclic 4-coloring of planar graphs without 4- and 5-cycles

Every planar graph is known to be acyclically 5-colorable (O.V.Borodin, 1976). Some sufficient conditions are also obtained for a planar graph to be acyclically 4- and 3-colorable. In particular, the acyclic 4-colorability was proved for the following planar graphs: without 3- and 4-cycles (O.V.Borodin, A.V. Kostochka, and D.R.Woodall, 1999), without 4-, 5-, and 6-cycles, or without 4-, 5-, and 7-cycles, or without 4-, 5-, and intersecting 3-cycles (M. Montassier, A.Raspaud andW.Wang, 2006), and without 4-, 5-, and 8-cycles (M. Chen and A.Raspaud, 2009). The purpose of this paper is to prove that each planar graph without 4- and 5-cycles is acyclically 4-colorable.     

Acyclic 4-colorability of planar graphs without cycles of length 4 or 6

Every planar graph is known to be acyclically 5-colorable (O. V. Borodin, 1976), which bound is precise. Some sufficient conditions are also obtained for a planar graph to be acyclically 4-colorable. In particular, the acyclic 4-colorabilitywas proved for the following planar graphs: without 3- and 4-cycles (O. V. Borodin, A. V. Kostochka, and D. R. Woodall, 1999), without 4-, 5-, and 6-cycles (M. Montassier, A. Raspaud, and W. Wang, 2006), and either without 4-, 6-, and 7-cycles or without 4-, 6-, and 8-cycles (M. Chen, A. Raspaud, and W. Wang, 2009). In this paper it is proved that each planar graph with neither 4-cycles nor 6-cycles is acyclically 4-colorable.     

Acyclic 5-choosability of planar graphs without 4-cycles

The conjecture on the acyclic 5-choosability of planar graphs (Borodin et al., 2002) as yet has been verified only for several restricted classes of graphs: those of girth at least 5 (Montassier, Ochem, and Raspaud, 2006), without 4- and 5-cycles or without 4- and 6-cycles (Montassier, Raspaud, and Wang, 2007), with neither 4-cycles nor chordal 6-cycles (Zhang and Xu, 2009), with neither 4- cycles nor two 3-cycles at distance less than 3 (Chen and Wang, 2008), and with neither 4-cycles nor intersecting 3-cycles (Chen and Raspaud, 2010). Wang and Chen (2009) proved that the planar graphs without 4-cycles are acyclically 6-choosable. We prove that a planar graph without 4-cycles is acyclically 5-choosable, which is a common strengthening of all above-mentioned results.     

A note on the acyclic 3-choosability of some planar graphs

An acyclic coloring of a graph G is a coloring of its vertices such that: (i) no two adjacent vertices in G receive the same color and (ii) no bicolored cycles exist in G. A list assignment of G is a function L that assigns to each vertex v∈V(G) a list L(v) of available colors. Let G be a graph and L be a list assignment of G. The graph G is acyclically L-list colorable if there exists an acyclic coloring ? of G such that ?(v)∈L(v) for all v∈V(G). If G is acyclically L-list colorable for any list assignment L with |L(v)|≥k for all v∈V(G), then G is said to be acyclically k-choosable. Borodin et al. proved that every planar graph with girth at least 7 is acyclically 3-choosable (Borodin et al., submitted for publication [4]). More recently, Borodin and Ivanova showed that every planar graph without cycles of length 4 to 11 is acyclically 3-choosable (Borodin and Ivanova, submitted for publication [7]). In this note, we connect these two results by a sequence of intermediate sufficient conditions that involve the minimum distance between 3-cycles: we prove that every planar graph with neither cycles of lengths 4 to 7 (resp. to 8, to 9, to 10) nor triangles at distance less than 7 (resp. 5, 3, 2) is acyclically 3-choosable.     

Planar graphs without triangles adjacent to cycles of length from 4 to 7 are 3-colorable

It is known that planar graphs without cycles of length from 4 to 7 are 3-colorable (Borodin et al., 2005) [13] and that planar graphs in which no triangles have common edges with cycles of length from 4 to 9 are 3-colorable (Borodin et al., 2006) [11]. We give a common extension of these results by proving that every planar graph in which no triangles have common edges with k-cycles, where k∈{4,5,7} (or, which is equivalent, with cycles of length 3, 5 and 7), is 3-colorable.     

Planar graphs without 3-, 7-, and 8-cycles are 3-choosable

A graph G is k-choosable if every vertex of G can be properly colored whenever every vertex has a list of at least k available colors. Grötzsch’s theorem [4] states that every planar triangle-free graph is 3-colorable. However, Voigt [M. Voigt, A not 3-choosable planar graph without 3-cycles, Discrete Math. 146 (1995) 325-328] gave an example of such a graph that is not 3-choosable, thus Grötzsch’s theorem does not generalize naturally to choosability. We prove that every planar triangle-free graph without 7- and 8-cycles is 3-choosable.     

A 3-color Theorem on Plane Graphs without 5-circuits

In this paper, we prove that every plane graph without 5-circuits and without triangles of distance less than 3 is 3-colorable. This improves the main result of Borodin and Raspaud [Borodin, O. V., Raspaud, A.： A sufficient condition for planar graphs to be 3-colorable. Journal of Combinatorial Theory, Ser. B, 88, 17-27 （2003）], and provides a new upper bound to their conjecture.     

On acyclic edge coloring of planar graphs without intersecting triangles

Let Δ denote the maximum degree of a graph. Fiam?ík first and then Alon et al. again conjectured that every graph is acyclically edge (Δ+2)-colorable. Even for planar graphs, this conjecture remains open. It is known that every triangle-free planar graph is acyclically edge (Δ+5)-colorable. This paper proves that every planar graph without intersecting triangles is acyclically edge (Δ+4)-colorable.     

Acyclic 4‐Choosability of Planar Graphs with No 4‐ and 5‐Cycles

Every planar graph is known to be acyclically 7‐choosable and is conjectured to be acyclically 5‐choosable (O. V. Borodin, D. G. Fon‐Der‐Flaass, A. V. Kostochka, E. Sopena, J Graph Theory 40 (2002), 83–90). This conjecture if proved would imply both Borodin's (Discrete Math 25 (1979), 211–236) acyclic 5‐color theorem and Thomassen's (J Combin Theory Ser B 62 (1994), 180–181) 5‐choosability theorem. However, as yet it has been verified only for several restricted classes of graphs. Some sufficient conditions are also obtained for a planar graph to be acyclically 4‐ and 3‐choosable. In particular, the acyclic 4‐choosability was proved for the following planar graphs: without 3‐, 4‐, and 5‐cycles (M. Montassier, P. Ochem, and A. Raspaud, J Graph Theory 51 (2006), 281–300), without 4‐, 5‐, and 6‐cycles, or without 4‐, 5‐, and 7‐cycles, or without 4‐, 5‐, and intersecting 3‐cycles (M. Montassier, A. Raspaud, W. Wang, Topics Discrete Math (2006), 473–491), and neither 4‐ and 5‐cycles nor 8‐cycles having a triangular chord (M. Chen and A. Raspaud, Discrete Math. 310(15–16) (2010), 2113–2118). The purpose of this paper is to strengthen these results by proving that each planar graph without 4‐ and 5‐cycles is acyclically 4‐choosable.     

平面图3色可染的一个充分条件

Steinberg猜想既没有4-圈又没有5-圈的平面图是3色可染的. Xu, Borodin等人各自独立地证明了既没有相邻三角形又没有5-和7-圈的平面图是3 色可染的. 作为这一结果的推论, 没有4-, 5-和7-圈的平面图是3色可染的. 本文证明一个比此推论更接近Steinberg猜想的结果, 设G是一个既没有4-圈又没有5-圈的平面图, 若对每一个k∈{3, 6, 7}, G都不含(k, 7)-弦, 则G是3色可染的, 这里的(k, 7)-弦是指长度为7+k-2的圈的一条弦, 它的两个端点将圈分成两条路, 一条路的长度为6, 另一条路的长度为k-1.     

A structural theorem on embedded graphs and its application to colorings

In this paper, a Lebesgue type theorem on the structure of graphs embedded in the surface of characteristic σ≤ 0 is given, that generalizes a result of Borodin on plane graphs. As a consequence, it is proved that every such graph without i-circuits for 4 ≤ i ≤ 11 - 3σ is 3-choosable, that offers a new upper bound to a question of Y. Zhao.     

Bordeaux 3-color conjecture and 3-choosability

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 4- and 5-cycles, and without triangles at distance less than 4, or without 4-, 5- and 6-cycles, and without triangles at distance less than 3 is 3-choosable; (2) there exists a non-3-choosable planar graph without 4-cycles, 5-cycles, and intersecting triangles. These results have some consequences on the Bordeaux 3-color conjecture by Borodin and Raspaud [A sufficient condition for planar graphs to be 3-colorable. J. Combin. Theory Ser. B 88 (2003) 17-27].     

Every planar graph without 4-cycles adjacent to two triangles is DP-4-colorable

Wang and Lih (2002) conjectured that every planar graph without adjacent triangles is 4-choosable. In this paper, we prove that every planar graph without any 4-cycle adjacent to two triangles is DP-4-colorable, which improves the results of Lam et al. (1999), Cheng et al. (2016) and Kim and Yu [ arXiv:1709.09809v1].     

Acyclic 6-choosability of planar graphs without adjacent short cycles

A proper vertex coloring of a graph G is acyclic if G contains no bicolored cycles.Given a list assignment L={L(v)|v∈V}of G,we say that G is acyclically L-colorable if there exists a proper acyclic coloringπof G such thatπ(v)∈L(v)for all v∈V.If G is acyclically L-colorable for any list assignment L with|L(v)|k for all v∈V(G),then G is acyclically k-choosable.In this paper,we prove that every planar graph G is acyclically 6-choosable if G does not contain 4-cycles adjacent to i-cycles for each i∈{3,4,5,6}.This improves the result by Wang and Chen(2009).     

On 3-colorable non-4-choosable planar graphs

An L-list coloring of a graph G is a proper vertex coloring in which every vertex v gets a color from a list L(v) of allowed colors. G is called k-choosable if all lists L(v) have exactly k elements and if G is L-list colorable for all possible assignments of such lists. Verifying conjectures of Erdos, Rubin and Taylor it was shown during the last years that every planar graph is 5-choosable and that there are planar graphs which are not 4-choosable. The question whether there are 3-colorable planar graphs which are not 4-choosable remained unsolved. The smallest known example far a non-4-choosable planar graph has 75 vertices and is described by Gutner. In fact, this graph is also 3 colorable and answers the above question. In addition, we give a list assignment for this graph using 5 colors only in all of the lists together such that the graph is not List-colorable. © 1997 John Wiley & Sons, Inc.     

Acyclic 5‐choosability of planar graphs without adjacent short cycles

The conjecture on acyclic 5‐choosability of planar graphs [Borodin et al., 2002] as yet has been verified only for several restricted classes of graphs. None of these classes allows 4‐cycles. We prove that a planar graph is acyclically 5‐choosable if it does not contain an i‐cycle adjacent to a j‐cycle where 3?j?5 if i = 3 and 4?j?6 if i = 4. This result absorbs most of the previous work in this direction. © 2010 Wiley Periodicals, Inc. J Graph Theory 68:169‐176, 2011     

Acyclic 5-choosability of planar graphs without 4-cycles

A proper vertex coloring of a graph G=(V,E) is acyclic if G contains no bicolored cycle. A graph G is acyclically L-list colorable if for a given list assignment L={L(v):v∈V}, there exists a proper acyclic coloring π of G such that π(v)∈L(v) for all v∈V. If G is acyclically L-list colorable for any list assignment with |L(v)|≥k for all v∈V, then G is acyclically k-choosable. In this paper we prove that every planar graph without 4-cycles and without two 3-cycles at distance less than 3 is acyclically 5-choosable. This improves a result in [M. Montassier, P. Ochem, A. Raspaud, On the acyclic choosability of graphs, J. Graph Theory 51 (2006) 281-300], which says that planar graphs of girth at least 5 are acyclically 5-choosable.     

Every planar graph without adjacent cycles of length at most 8 is 3-choosable

DP-coloring as a generalization of list coloring was introduced by Dvořák and Postle in 2017, who proved that every planar graph without cycles from 4 to 8 is 3-choosable, which was conjectured by Borodin et al. in 2007. In this paper, we prove that every planar graph without adjacent cycles of length at most 8 is 3-choosable, which extends this result of Dvořák and Postle.