proposition: Lemma tanK : {in `](- (pi / 2)), (pi / 2)[ , cancel tan atan}.
proof: Proof. move=> x xB; apply tan_inj => //; rewrite ?atanK//. by rewrite in_itv/= atan_gtNpi2 atan_ltpi2. 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