proposition: Lemma atan0 : atan 0 = 0 :> R.
proof: Proof. apply: tan_inj; last by rewrite atanK tan0. - by rewrite in_itv/= atan_gtNpi2 atan_ltpi2. - by rewrite in_itv/= oppr_cp0 divr_gt0 ?pi_gt0. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) reals ereal nsatz_realtype signed topology normedtype landau sequences derive realfun exp