theorem Th10: :: INTEGR14:10

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