© 1988 by London Mathematical Society
© The London Mathematical Society
Isomorphic Factorization of Regular Graphs and 3-Regular Multigraphs
Department of Combinatorics, and Optimization, University of Waterloo Waterloo, Ontario N2L 3GI, Canada
Department of Mathematics, University of Auckland Private Bag, Auckland, New Zealand
Received 5 November 1984. Revision received 17 February 1987.
A multigraph G is divisible by t if its edge set can be partitioned into t subsets, such that the subgraphs (called factors) induced by the subsets are all isomorphic. If G has e(G) edges, then it is t-rational if it is divisible by t or if t does not divide e(G). A short proof is given that any graph G is t-rational for all t
'(G) (the chromatic index of G), and thus any r-regular graph is t-rational for all t
r+1. The main result of this paper is that all 3-regular multigraphs are divisible by 3, in such a way that the components of each factor are paths of length 1 or 2. It follows that 3-regular graphs are t-rational for all t
3. The proofs rely on edge-colouring techniques.
Current address: Department of Mathematics, Vanderbilt University, Nashville, Tennessee 37235, USA