theorem Th6: :: PDIFF_4:6

for x, y, z being Real
for u being Element of REAL 3
for f being PartFunc of (REAL 3),REAL st u = <*x,y,z*> & f is_partial_differentiable_in u,3 holds
SVF1 (3,f,u) is_differentiable_in z by Th3;