for f1, f2 being PartFunc of REAL,REAL
for x0 being Real st f1 is_right_differentiable_in x0 & f2 is_right_differentiable_in x0 holds
( f1 (#) f2 is_right_differentiable_in x0 & Rdiff ((f1 (#) f2),x0) = ((Rdiff (f1,x0)) * (f2 . x0)) + ((Rdiff (f2,x0)) * (f1 . x0)) )