theorem :: DIFF_4:10

for x0, x1 being Real st x0 in dom cosec & x1 in dom cosec holds
[!(cosec (#) cosec),x0,x1!] = (4 * ((sin (x1 + x0)) * (sin (x1 - x0)))) / ((((cos (x0 + x1)) - (cos (x0 - x1))) ^2) * (x0 - x1))