theorem Th6: :: PDIFF_3:6

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`12_in z holds
hpartdiff12 (f,z) = diff ((SVF1 (2,(pdiff1 (f,1)),z)),y0)