proposition: Lemma imset_id (T : finType) (A : {set T}) : [set x | x in A] = A.
proof: Proof. by apply/setP=> x; rewrite (@can_imset_pre _ _ id) ?inE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)