© 1999 by London Mathematical Society
© The London Mathematical Society
Acyclic Colourings of Planar Graphs with Large Girth
Institute of Mathematics, Siberian Branch, Russian Academy of Sciences Novosibirsk 630090, Russia
Novosibirsk State University Novosibirsk 630090, Russia
Department of Mathematics, University of Nottingham Nottingham NG7 2RD
Received 20 December 1995. Revision received 26 October 1997.
A proper vertex-colouring of a graph is acyclic if there are no 2-coloured cycles. It is known that every planar graph is acyclically 5-colourable, and that there are planar graphs with acyclic chromatic number
a = 5 and girth g = 4. It is proved here that a planar graph satisfies
a
4 if g
5 and
a
3 if g
7.