let u0 be Element of REAL 3; :: thesis: for f1, f2 being PartFunc of (REAL 3),REAL st f1 is_hpartial_differentiable`23_in u0 & f2 is_hpartial_differentiable`23_in u0 holds
( (pdiff1 (f1,2)) + (pdiff1 (f2,2)) is_partial_differentiable_in u0,3 & partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (hpartdiff23 (f1,u0)) + (hpartdiff23 (f2,u0)) )
let f1, f2 be PartFunc of (REAL 3),REAL; :: thesis: ( f1 is_hpartial_differentiable`23_in u0 & f2 is_hpartial_differentiable`23_in u0 implies ( (pdiff1 (f1,2)) + (pdiff1 (f2,2)) is_partial_differentiable_in u0,3 & partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (hpartdiff23 (f1,u0)) + (hpartdiff23 (f2,u0)) ) )
assume that
A1: f1 is_hpartial_differentiable`23_in u0 and
A2: f2 is_hpartial_differentiable`23_in u0 ; :: thesis: ( (pdiff1 (f1,2)) + (pdiff1 (f2,2)) is_partial_differentiable_in u0,3 & partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (hpartdiff23 (f1,u0)) + (hpartdiff23 (f2,u0)) )
A3: pdiff1 (f1,2) is_partial_differentiable_in u0,3 by A1, Th24;
A4: pdiff1 (f2,2) is_partial_differentiable_in u0,3 by A2, Th24;
then ( (pdiff1 (f1,2)) + (pdiff1 (f2,2)) is_partial_differentiable_in u0,3 & partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (partdiff ((pdiff1 (f1,2)),u0,3)) + (partdiff ((pdiff1 (f2,2)),u0,3)) ) by A3, PDIFF_1:29;
then partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (hpartdiff23 (f1,u0)) + (partdiff ((pdiff1 (f2,2)),u0,3)) by A1, Th33
.= (hpartdiff23 (f1,u0)) + (hpartdiff23 (f2,u0)) by A2, Th33 ;
hence ( (pdiff1 (f1,2)) + (pdiff1 (f2,2)) is_partial_differentiable_in u0,3 & partdiff (((pdiff1 (f1,2)) + (pdiff1 (f2,2))),u0,3) = (hpartdiff23 (f1,u0)) + (hpartdiff23 (f2,u0)) ) by A3, A4, PDIFF_1:29; :: thesis: verum