proposition: Lemma seqs1 : forall f injf, sop (@perm _ f injf) = map f ecubes.
proof: Proof. move=> f ?; rewrite ecubes_def /sop /= -codom_ffun pvalE. by apply: eq_codom; apply: permE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop finset fingroup) mathcomp(action perm primitive_action)