Discrepancy in arithmetic progressions

It is proven that there is a two-coloring of the first n integers for which all arithmetic progressions have discrepancy less than const.n1/4. This shows that a 1964 result of K. F. Roth is, up to constants, best possible. Department of Applied Mathematics, Charles University, Malostranske nam. 25, 118 00 Praha 1, Czech Republic E-mail address: matousek@kam.mff.cuni.cz Courant Institute of Mathematical Sciences, 251 Mercer Street, New York, New York 10012 E-mail address: spencer@cs.nyu.edu License or copyright restrictions may apply to redistribution; see http://www.ams.org/journal-terms-of-use