proposition: Lemma fset_notin_join X Y x : x ∉ X ⊔ Y ↔ x ∉ X ∧ x ∉ Y.
proof: Proof. rewrite fset_in_join. tauto. Qed.
imports: MathClasses.theory.lattices MathClasses.varieties.monoids MathClasses.implementations.bool MathClasses.implementations.list_finite_set MathClasses.orders.lattices MathClasses.interfaces.abstract_algebra MathClasses.interfaces.finite_sets MathClasses.interfaces.orders