The introduced set-theoretical concepts allow us to formulate a famous lemma which was stated by Max Zorn (1906 - 1993).

Lemma: Zorn's Lemma

If every chain $S\subseteq X$ in a poset $(V,\preceq )$ has an upper bound, then the poset $V$ contains at least one maximal element.

Proofs: 1

Proofs: 1
Propositions: 2

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