proposition: Fact lex1 t : t <= [tuple of nseq n \top].
proof: Proof. by apply: sub_seqprod_lexi; apply: lex1 (t : n.-tupleprod T). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)