Abstrakt: |
Abstract  Consider the set of all proper edge-colourings of a graph G with n colours. Among all such colourings, the minimum length of a longest two-coloured cycle is denoted L(n, G). The problem of understanding L(n, G) was posed by Häggkvist in 1978 and, specifically, L(n, K n,n ) has received recent attention. Here we construct, for each prime power q ⥠8, an edge-colouring of K n,n with n colours having all two-coloured cycles of length ⤠2q 2, for integers n in a set of density 1 â 3/(q â 1). One consequence is that L(n, K n,n ) is bounded above by a polylogarithmic function of n, whereas the best known general upper bound was previously 2n â 4. [ABSTRACT FROM AUTHOR] |