proposition: Corollary slice_kkxx s k : &:s `[k, k] = oapp (cons^~ [::]) [::] (onth s k).
proof: Proof. by rewrite slice_kk. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext)