theorem :: PDIFF_4:28

for u0 being Element of REAL 3
for f1, f2 being PartFunc of (REAL 3),REAL st f1 is_partial_differentiable_in u0,1 & f2 is_partial_differentiable_in u0,1 holds
f1 (#) f2 is_partial_differentiable_in u0,1