Information Processing Letters 115 (2015) 263–268
Contents lists available at ScienceDirect
Information Processing Letters
www.elsevier.com/locate/ipl
Adjacent-vertex-distinguishing proper edge colorings of
planar bipartite graphs with = 9, 10, or 11
✩
Xiang’en Chen
∗
, Zepeng Li
College of Mathematics and Statistics, Northwest Normal University, Lanzhou 730070, PR China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
23 February 2013
Received
in revised form 24 September
2014
Accepted
24 September 2014
Available
online 2 October 2014
Communicated
by Jinhui Xu
Keywords:
Combinatorial
problems
Graphs
Planar
bipartite graphs
Adjacent-vertex-distinguishing
proper edge
coloring
Adjacent-vertex-distinguishing
proper edge
chromatic number
It is obtained in this paper by using of discharging method that the adjacent-vertex-
distinguishing
proper edge chromatic number χ
a
(G) ≤ (G) + 1for any planar bipartite
graph G with maximum degree (G) = 9, 10, or 11 and no component K
2
. This expands a
result which belongs to K. Edwards, M. Hor
ˇ
nák, M. Wo ´zniak.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Adjacent-vertex-distinguishing proper edge coloring of
graph is one of the important combinatorial problems. Let
G be a finite, undirect simple graph with no component K
2
and denote by (G) the maximum degree of G, where K
2
is the complete graph of order 2. Let C ={1, 2, ···, k} be
a finite set of colors and let f : E(G) −→ C be a k-proper
edge coloring of G. The color set of a vertex v ∈ V (G) with
respect to f , in symbols S
f
(v), is the set of colors of edges
incident with v, i.e., S
f
(v) ={f (vw) | vw ∈ E(G)}. The
k-proper edge coloring f of G is called k-adjacent-vertex-
distinguishing
(k-AVDPEC for short) if it distinguishes any
two adjacent vertices by their color sets, i.e., S
f
(u) =
S
f
(v) for ∀u, v ∈ V (G), uv ∈ E(G), the number χ
a
(G) =
✩
This research is supported by NNSFC (No. 61163037, 61163054,
61363060).
*
Corresponding author.
E-mail
address: chenxe@nwnu.edu.cn (X. Chen).
min{k | G has a k-AVDPEC} is called the adjacent-vertex-
distinguishing
proper edge chromatic number of G.
The
theory of vertex-distinguishing proper edge color-
ing
has been investigated in several papers [1,3]. Adjacent
strong edge coloring (i.e., adjacent-vertex-distinguishing
proper edge coloring) is considered in [6] by Zhongfu
Zhang et al. and some special families of graphs are dis-
cussed,
at the same time, the following conjecture was
proposed by the authors of [6].
Conjecture
1. Let Gbe simple connected graph with order at
least 6, then χ
a
(G) ≤ (G) + 2.
The
following results have been proved in [2]: χ
a
(G) ≤ 5
for
such graphs with maximum degree (G) = 3with
no isolated edges and χ
a
(G) ≤ (G) + 2for bipartite
graph G with no isolated edges. These bounds are tight.
For k-chromatic graph G without isolated edges, χ
a
(G) =
(
G) + O(log k).
The
authors of [5] got the following result: For any pla-
nar
bipartite graph G with maximum degree (G) ≥ 12
http://dx.doi.org/10.1016/j.ipl.2014.09.025
0020-0190/
© 2014 Elsevier B.V. All rights reserved.