Zermelo-Fraenkel Set Theory

Zermelo-Fraenkel set theory with the Axiom of Choice (ZFC) is the standard foundation of modern mathematics — the axiomatic system within which virtually all contemporary mathematical theorems are formalized, proved, and understood. It is not merely a branch of set theory but the ambient logical environment in which analysis, algebra, topology, and even parts of computer science operate. To say that a theorem is true