let u0 be Element of REAL 3; :: thesis: for f1, f2 being PartFunc of (REAL 3),REAL st f1 is_hpartial_differentiable`21_in u0 & f2 is_hpartial_differentiable`21_in u0 holds
( (pdiff1 (f1,2)) - (pdiff1 (f2,2)) is_partial_differentiable_in u0,1 & partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (hpartdiff21 (f1,u0)) - (hpartdiff21 (f2,u0)) )
let f1, f2 be PartFunc of (REAL 3),REAL; :: thesis: ( f1 is_hpartial_differentiable`21_in u0 & f2 is_hpartial_differentiable`21_in u0 implies ( (pdiff1 (f1,2)) - (pdiff1 (f2,2)) is_partial_differentiable_in u0,1 & partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (hpartdiff21 (f1,u0)) - (hpartdiff21 (f2,u0)) ) )
assume that
A1: f1 is_hpartial_differentiable`21_in u0 and
A2: f2 is_hpartial_differentiable`21_in u0 ; :: thesis: ( (pdiff1 (f1,2)) - (pdiff1 (f2,2)) is_partial_differentiable_in u0,1 & partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (hpartdiff21 (f1,u0)) - (hpartdiff21 (f2,u0)) )
A3: pdiff1 (f1,2) is_partial_differentiable_in u0,1 by A1, Th22;
A4: pdiff1 (f2,2) is_partial_differentiable_in u0,1 by A2, Th22;
then ( (pdiff1 (f1,2)) - (pdiff1 (f2,2)) is_partial_differentiable_in u0,1 & partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (partdiff ((pdiff1 (f1,2)),u0,1)) - (partdiff ((pdiff1 (f2,2)),u0,1)) ) by A3, PDIFF_1:31;
then partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (hpartdiff21 (f1,u0)) - (partdiff ((pdiff1 (f2,2)),u0,1)) by A1, Th31
.= (hpartdiff21 (f1,u0)) - (hpartdiff21 (f2,u0)) by A2, Th31 ;
hence ( (pdiff1 (f1,2)) - (pdiff1 (f2,2)) is_partial_differentiable_in u0,1 & partdiff (((pdiff1 (f1,2)) - (pdiff1 (f2,2))),u0,1) = (hpartdiff21 (f1,u0)) - (hpartdiff21 (f2,u0)) ) by A3, A4, PDIFF_1:31; :: thesis: verum