(mathematics) Of or relating to Zermelo-Fraenkel set theory.

(game theory) A theorem about finite two-person games of perfect information in which the players move alternately and chance does not affect the decision-making process. It states that if the game cannot end in a draw, then one of the two players must have a winning strategy, i.e. force a win.

(set theory) An early and influential axiomatisation of set theory.

(mathematics) An axiomatic system that was proposed in the early 20th century in order to formulate a theory of sets free from paradoxes such as Russell's paradox, and became the standard form of axiomatic set theory.