let x0, y0, z0 be Real; for u being Element of REAL 3
for f being PartFunc of (REAL 3),REAL st u = <*x0,y0,z0*> & f is_hpartial_differentiable`23_in u holds
hpartdiff23 (f,u) = diff ((SVF1 (3,(pdiff1 (f,2)),u)),z0)
let u be Element of REAL 3; for f being PartFunc of (REAL 3),REAL st u = <*x0,y0,z0*> & f is_hpartial_differentiable`23_in u holds
hpartdiff23 (f,u) = diff ((SVF1 (3,(pdiff1 (f,2)),u)),z0)
let f be PartFunc of (REAL 3),REAL; ( u = <*x0,y0,z0*> & f is_hpartial_differentiable`23_in u implies hpartdiff23 (f,u) = diff ((SVF1 (3,(pdiff1 (f,2)),u)),z0) )
set r = hpartdiff23 (f,u);
assume that
A1:
u = <*x0,y0,z0*>
and
A2:
f is_hpartial_differentiable`23_in u
; hpartdiff23 (f,u) = diff ((SVF1 (3,(pdiff1 (f,2)),u)),z0)
consider x1, y1, z1 being Real such that
A3:
( u = <*x1,y1,z1*> & ex N being Neighbourhood of z1 st
( N c= dom (SVF1 (3,(pdiff1 (f,2)),u)) & ex L being LinearFunc ex R being RestFunc st
for z being Real st z in N holds
((SVF1 (3,(pdiff1 (f,2)),u)) . z) - ((SVF1 (3,(pdiff1 (f,2)),u)) . z1) = (L . (z - z1)) + (R . (z - z1)) ) )
by A2;
consider N being Neighbourhood of z1 such that
A4:
( N c= dom (SVF1 (3,(pdiff1 (f,2)),u)) & ex L being LinearFunc ex R being RestFunc st
for z being Real st z in N holds
((SVF1 (3,(pdiff1 (f,2)),u)) . z) - ((SVF1 (3,(pdiff1 (f,2)),u)) . z1) = (L . (z - z1)) + (R . (z - z1)) )
by A3;
consider L being LinearFunc, R being RestFunc such that
A5:
for z being Real st z in N holds
((SVF1 (3,(pdiff1 (f,2)),u)) . z) - ((SVF1 (3,(pdiff1 (f,2)),u)) . z1) = (L . (z - z1)) + (R . (z - z1))
by A4;
A6:
( x0 = x1 & y0 = y1 & z0 = z1 )
by A1, A3, FINSEQ_1:78;
A7:
hpartdiff23 (f,u) = L . 1
by A2, A3, A4, A5, Def15;
SVF1 (3,(pdiff1 (f,2)),u) is_differentiable_in z0
by A4, A6, FDIFF_1:def 4;
hence
hpartdiff23 (f,u) = diff ((SVF1 (3,(pdiff1 (f,2)),u)),z0)
by A4, A5, A6, A7, FDIFF_1:def 5; verum