proposition: Lemma negb_and3 (a b c : bool) : ~~ (a && b && c) = ~~ a || ~~ b || ~~ c.
proof: Proof. by case: a; case: b; case: c. Qed.
imports: mathcomp.ssreflect.ssreflect mathcomp(ssrbool ssrfun ssrnat eqtype choice seq) mathcomp(fintype finset finfun bigop order) mathcomp(ssralg ssrnum path generic_quotient matrix mxalgebra) mathcomp(zmodp) GeoCoq.Meta_theory.Models.POF_to_Tarski GeoCoq.Meta_theory.Counter_models.Planar.independence