(topology) A topological game invented by the Polish mathematician Mazur in order to illustrate the difference between sets of the first category and second category.

In the Mazur game, the unit interval [0,1] is initially divided into two complementary sets, A and B. Player 1 then chooses a closed interval in [0,1] of length $\leq {1 \over 2}$ and greater than zero. Player 2 then chooses an interval within the previously chosen interval, of length $\leq {1 \over 3}$ and greater than zero. Player 1 then chooses an interval within the previous interval, of length $\leq {1 \over 4}$ and greater than zero, and so on. After infinitely many steps, the intersection of all the chosen intervals is a single point: if it falls within set A, then player 1 wins; if it falls within set B, player 2 wins.