theorem :: FDIFF_8:17

for Z being open Subset of REAL st Z c= dom (exp_R * cot) holds
( exp_R * cot is_differentiable_on Z & ( for x being Real st x in Z holds
((exp_R * cot) `| Z) . x = - ((exp_R . (cot . x)) / ((sin . x) ^2)) ) )