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(*  Maximum and minimun (sub)set with respect to a given pred         *)
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Section MaxSetMinSet.
Variable T : finType.
Notation sT := {set T}.
Implicit Types A B C : sT.
Implicit Type P : pred sT.
Definition minset P A := [forall (B : sT | B \subset A), (B == A) == P B].

Lemma minset_exists P C : P C -> {A | minset P A & A \subset C}.
Fact maxset_key : unit. Proof. by []. Qed.