proposition: Lemma slice0 i : &:([::] : seq A) i = [::].
proof: Proof. by rewrite /slice /=; case: i=>[[[] av|[]]]; case=>[[] bv|[]]. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext)