proposition: Lemma domU1 z : dom (<< z >> : {freeg K / R}) = [:: z].
proof: Proof. by rewrite domU ?oner_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)