The Game of Normal Numbers

We introduce a two-player game where at each period one player, say, Player 2, chooses a distribution and the other player, Player 1, chooses a realization. Player 1 wins the game if the sequence of realized outcomes is normal with respect to the sequence of distributions. We present a pure winning strategy of Player 1 and thereby provide a universal algorithm that generates a normal sequence for any discrete stochastic process. It turns out that to select the nth digit, the algorithm conducts O(n²) calculations. The proof uses approachability in infinite-dimensional spaces (Lehrer 2002).