for m, n being non zero Element of NAT
for f being PartFunc of (REAL m),(REAL n)
for g being PartFunc of (REAL-NS m),(REAL-NS n)
for X being Subset of (REAL m)
for Y being Subset of (REAL-NS m)
for i being Nat st 1 <= i & i <= m & X is open & g = f & X = Y & f is_partial_differentiable_on X,i holds
for x0, x1 being Element of REAL m
for y0, y1 being Point of (REAL-NS m) st x0 = y0 & x1 = y1 & x0 in X & x1 in X holds
|.(((f `partial| (X,i)) /. x1) - ((f `partial| (X,i)) /. x0)).| = ||.(((g `partial| (Y,i)) /. y1) - ((g `partial| (Y,i)) /. y0)).||