theorem :: PDIFF_2:13

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_partial_differentiable_in z,1 holds
partdiff (f,z,1) = diff ((SVF1 (1,f,z)),x0)