How to Gamble Against All Odds

Abstract: We compare the prediction power of betting strategies (aka martingales) whose wagers take values in different sets of reals. A martingale whose wagers take values in a set A is called an A-martingale. A set of reals B anticipates a set A, if for every A-martingale there is a countable set of B-martingales, such that on every binary sequence on which the A-martingale gains an infinite amount at least one of the B-martingales gains an infinite amount, too.
We show that for a wide class of pairs of sets A and B, B anticipates A if and only if A is a subset of the closure of rB, for some r > 0, e.g., when B is well ordered (has no left-accumulation points). Our results answer a question posed by Chalcraft et al. (2012).