theorem :: SIN_COS9:127

for Z being open Subset of REAL st Z c= dom (ln (#) arctan) & Z c= ].(- 1),1.[ holds
( ln (#) arctan is_differentiable_on Z & ( for x being Real st x in Z holds
((ln (#) arctan) `| Z) . x = ((arctan . x) / x) + ((ln . x) / (1 + (x ^2))) ) )