Source: wikibot/non-well-founded-set-theory
= Non-well-founded set theory
{wiki=Non-well-founded_set_theory}
Non-well-founded set theory is a branch of set theory that allows for sets that can contain themselves as elements, either directly or indirectly, leading to the formation of infinite descending chains. This is in contrast to classical set theory, particularly Zermelo-Fraenkel set theory with the Axiom of Foundation (or Axiom of Regularity), which restricts sets to be well-founded.