proposition: Lemma itv_lex1 i : i <= `]-oo, +oo[.
proof: Proof. by case: i => [?[|[]]]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)