theorem :: FDIFF_11:41

for Z being open Subset of REAL st Z c= ].(- 1),1.[ holds
( cos (#) (arctan + arccot) is_differentiable_on Z & ( for x being Real st x in Z holds
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x))) ) )