proposition: Lemma size_prop1 a b n c (l:= size (cons a b n c)): [/\ size a < l, size b < l, size c < l & size [a, b] <= l]%N.
proof: Proof. rewrite /= !ltnS leq_maxl maxnCA leq_maxl maxnC - maxnA maxnC - maxnA leq_maxl. by rewrite -/size maxn0 maxnC leq_maxr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)