proposition: Lemma fset_join_singletons x : {{ x ; x }} = {{ x }}.
proof: Proof. now rewrite (idempotency (⊔) _). 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