proposition: Lemma sub1b x: T1nf x -> x = (one + x) - one.
proof: Proof. case:x => // a n b; case: a => //; rewrite T1nf_finite1 => /eqP -> //. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)