proposition: Lemma fset0Vmem X : ( X = fset0 ) + { x | x \in X }.
proof: Proof. case: X => [[|x xs] ax_xs];[left|right;exists x;exact: mem_head]. apply: fset_ext => x; by rewrite inE !unfold_in. Qed.
imports: Recdef mathcomp(all_ssreflect) CompDecModal.libs(edone bcase base)