theorem Th5: :: PDIFF_4:5

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,2 holds
SVF1 (2,f,u) is_differentiable_in y by Th2;