theorem :: DIFF_3:89

for x0, x1 being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = (cot (#) sin) . x ) & x0 in dom cot & x1 in dom cot holds
[!f,x0,x1!] = ((cos x0) - (cos x1)) / (x0 - x1)