proposition: Lemma acosK : {in `[(-1),1], cancel acos cos}.
proof: Proof. by move=> x; rewrite in_itv/==> /acos_def[/andP[]]. 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