Analysis of information sources in references of the Wikipedia article "Ultrafilter on a set" in English language version.
Theorem 1.2. BPI [the Boolean Prime Ideal Theorem] & KM [Krein-Milman] (*) [the unit ball of the dual of a normed vector space has an extreme point].... Theorem 2.1. (*) AC [the Axiom of Choice].
Theorem 1.2. BPI [the Boolean Prime Ideal Theorem] & KM [Krein-Milman] (*) [the unit ball of the dual of a normed vector space has an extreme point].... Theorem 2.1. (*) AC [the Axiom of Choice].