Arithmetic Progressions of Cycle Lengths in Graphs

A recently posed question of Haggkvist and Scott's asked whether or not there exists a constant c such that if G is a graph of minimum degree ck then G contains cycles of k consecutive even lengths. In this paper we answer the question by proving that for k > 1, a bipartite graph of average degree at least 4k and girth g contains cycles of (g/2-1)k consecutive even lengths. We also obtain a short proof of the theorem of Bondy and Simonovits, that a graph of order n and size at least 8(k-1)n^{1 + 1/k} has a cycle of length 2k.