proposition: Lemma onem_neq0 (r : R) : (`1-r != 0) <-> (r != 1).
proof: Proof. by split; apply: contra => /eqP/onem_eq0/eqP. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum) mathcomp(reals normedtype) mathcomp(mathcomp_extra boolp) mathcomp(lra ring Rstruct)