theorem :: PDIFF_3:4

for x0, y0 being Real
for z being Element of REAL 2
for f being PartFunc of (REAL 2),REAL st z = <*x0,y0*> & f is_hpartial_differentiable`22_in z holds
SVF1 (2,(pdiff1 (f,2)),z) is_differentiable_in y0