let f be PartFunc of (REAL 2),REAL; :: thesis:
let z0 be Element of REAL 2; :: thesis:
let N be Neighbourhood of (proj (2,2)) . z0; :: thesis:
assume that
A1: f is_partial_differentiable_in z0,2 and
A2: N c= dom (SVF1 (2,f,z0)) ; :: thesis:
consider x0, y0 being Real such that
A3: z0 = <*x0,y0*> and
A4: ex N1 being Neighbourhood of y0 st
( N1 c= dom (SVF1 (2,f,z0)) & ex L being LinearFunc ex R being RestFunc st
for y being Real st y in N1 holds
((SVF1 (2,f,z0)) . y) - ((SVF1 (2,f,z0)) . y0) = (L . (y - y0)) + (R . (y - y0)) ) by A1, Th10;
consider N1 being Neighbourhood of y0 such that
N1 c= dom (SVF1 (2,f,z0)) and
A5: ex L being LinearFunc ex R being RestFunc st
for y being Real st y in N1 holds
((SVF1 (2,f,z0)) . y) - ((SVF1 (2,f,z0)) . y0) = (L . (y - y0)) + (R . (y - y0)) by A4;
A6: (proj (2,2)) . z0 = y0 by A3, Th2;
then consider N2 being Neighbourhood of y0 such that
A7: N2 c= N and
A8: N2 c= N1 by RCOMP_1:17;
A9: N2 c= dom (SVF1 (2,f,z0)) by A2, A7;
let h be non-zero 0 -convergent Real_Sequence; :: thesis:
let c be constant Real_Sequence; :: thesis:
assume that
A10: rng c = {((proj (2,2)) . z0)} and
A11: rng (h + c) c= N ; :: thesis:
consider g being Real such that
A12: 0 < g and
A13: N2 = ].(y0 - g),(y0 + g).[ by RCOMP_1:def 6;
( y0 + 0 < y0 + g & y0 - g < y0 - 0 ) by A12, XREAL_1:8, XREAL_1:44;
then A14: y0 in N2 by A13;
A15: rng c c= dom (SVF1 (2,f,z0))

let y be object ; :: according to TARSKI:def 3 :: thesis:
assume y in rng c ; :: thesis:
then y = y0 by A10, A6, TARSKI:def 1;
then y in N by A7, A14;
hence y in dom (SVF1 (2,f,z0)) by A2; :: thesis:

end;

ex n being Element of NAT st
( rng (c ^\ n) c= N2 & rng ((h + c) ^\ n) c= N2 )

proof

y0 in rng c by A10, A6, TARSKI:def 1;
then A16: lim c = y0 by SEQ_4:25;
lim h = 0 ;
then lim (h + c) = 0 + y0 by A16, SEQ_2:6
.= y0 ;
then consider n being Nat such that
A17: for m being Nat st n <= m holds
|.(((h + c) . m) - y0).| < g by A12, SEQ_2:def 7;
reconsider n = n as Element of NAT by ORDINAL1:def 12;
take n ; :: thesis:
A18: rng (c ^\ n) = {y0} by A10, A6, VALUED_0:26;
thus rng (c ^\ n) c= N2 by A14, A18, TARSKI:def 1; :: thesis:
let y be object ; :: according to TARSKI:def 3 :: thesis:
assume y in rng ((h + c) ^\ n) ; :: thesis:
then consider m being Element of NAT such that
A19: y = ((h + c) ^\ n) . m by FUNCT_2:113;
n + 0 <= n + m by XREAL_1:7;
then A20: |.(((h + c) . (n + m)) - y0).| < g by A17;
then ((h + c) . (m + n)) - y0 < g by SEQ_2:1;
then (((h + c) ^\ n) . m) - y0 < g by NAT_1:def 3;
then A21: ((h + c) ^\ n) . m < y0 + g by XREAL_1:19;
- g < ((h + c) . (m + n)) - y0 by A20, SEQ_2:1;
then - g < (((h + c) ^\ n) . m) - y0 by NAT_1:def 3;
then y0 + (- g) < ((h + c) ^\ n) . m by XREAL_1:20;
hence y in N2 by A13, A19, A21; :: thesis:

end;

then consider n being Element of NAT such that
rng (c ^\ n) c= N2 and
A22: rng ((h + c) ^\ n) c= N2 ;
consider L being LinearFunc, R being RestFunc such that
A23: for y being Real st y in N1 holds
((SVF1 (2,f,z0)) . y) - ((SVF1 (2,f,z0)) . y0) = (L . (y - y0)) + (R . (y - y0)) by A5;
A24: rng (c ^\ n) c= dom (SVF1 (2,f,z0))

proof

let y be object ; :: according to TARSKI:def 3 :: thesis:
assume A25: y in rng (c ^\ n) ; :: thesis:
rng (c ^\ n) = rng c by VALUED_0:26;
then y = y0 by A10, A6, A25, TARSKI:def 1;
then y in N by A7, A14;
hence y in dom (SVF1 (2,f,z0)) by A2; :: thesis:

end;

A26: L is total by FDIFF_1:def 3;
A27: ( ((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ") is convergent & lim (((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ")) = L . 1 )

proof

deffunc H₁( Nat) -> set = (L . 1) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . $1);
consider s1 being Real_Sequence such that
A28: for k being Nat holds s1 . k = H₁(k) from SEQ_1:sch 1();

A29: now :: thesis:

A30: ( ((h ^\ n) ") (#) (R /* (h ^\ n)) is convergent & lim (((h ^\ n) ") (#) (R /* (h ^\ n))) = 0 ) by FDIFF_1:def 2;
let r be Real; :: thesis:
assume 0 < r ; :: thesis:
then consider m being Nat such that
A31: for k being Nat st m <= k holds
|.(((((h ^\ n) ") (#) (R /* (h ^\ n))) . k) - 0).| < r by A30, SEQ_2:def 7;
take n1 = m; :: thesis:
let k be Nat; :: thesis:
assume A32: n1 <= k ; :: thesis:
|.((s1 . k) - (L . 1)).| = |.(((L . 1) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . k)) - (L . 1)).| by A28
.= |.(((((h ^\ n) ") (#) (R /* (h ^\ n))) . k) - 0).| ;
hence |.((s1 . k) - (L . 1)).| < r by A31, A32; :: thesis:

end;

consider s being Real such that
A33: for p1 being Real holds L . p1 = s * p1 by FDIFF_1:def 3;
A34: L . 1 = s * 1 by A33
.= s ;

now :: thesis:

let m be Element of NAT ; :: thesis:
A35: (h ^\ n) . m <> 0 by SEQ_1:5;
thus (((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ")) . m = (((L /* (h ^\ n)) + (R /* (h ^\ n))) . m) * (((h ^\ n) ") . m) by SEQ_1:8
.= (((L /* (h ^\ n)) . m) + ((R /* (h ^\ n)) . m)) * (((h ^\ n) ") . m) by SEQ_1:7
.= (((L /* (h ^\ n)) . m) * (((h ^\ n) ") . m)) + (((R /* (h ^\ n)) . m) * (((h ^\ n) ") . m))
.= (((L /* (h ^\ n)) . m) * (((h ^\ n) ") . m)) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m) by SEQ_1:8
.= (((L /* (h ^\ n)) . m) * (((h ^\ n) . m) ")) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m) by VALUED_1:10
.= ((L . ((h ^\ n) . m)) * (((h ^\ n) . m) ")) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m) by A26, FUNCT_2:115
.= ((s * ((h ^\ n) . m)) * (((h ^\ n) . m) ")) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m) by A33
.= (s * (((h ^\ n) . m) * (((h ^\ n) . m) "))) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m)
.= (s * 1) + (((R /* (h ^\ n)) (#) ((h ^\ n) ")) . m) by A35, XCMPLX_0:def 7
.= s1 . m by A28, A34 ; :: thesis:

end;

then A36: ((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ") = s1 by FUNCT_2:63;
hence ((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ") is convergent by A29, SEQ_2:def 6; :: thesis:
hence lim (((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ")) = L . 1 by A36, A29, SEQ_2:def 7; :: thesis:

end;

A37: rng ((h + c) ^\ n) c= dom (SVF1 (2,f,z0)) by A22, A7, A2;
A38: rng (h + c) c= dom (SVF1 (2,f,z0)) by A11, A2;
A39: for k being Element of NAT holds ((SVF1 (2,f,z0)) . (((h + c) ^\ n) . k)) - ((SVF1 (2,f,z0)) . ((c ^\ n) . k)) = (L . ((h ^\ n) . k)) + (R . ((h ^\ n) . k))

proof

let k be Element of NAT ; :: thesis:
((h + c) ^\ n) . k in rng ((h + c) ^\ n) by VALUED_0:28;
then A40: ((h + c) ^\ n) . k in N2 by A22;
( (c ^\ n) . k in rng (c ^\ n) & rng (c ^\ n) = rng c ) by VALUED_0:26, VALUED_0:28;
then A41: (c ^\ n) . k = y0 by A10, A6, TARSKI:def 1;
(((h + c) ^\ n) . k) - ((c ^\ n) . k) = (((h ^\ n) + (c ^\ n)) . k) - ((c ^\ n) . k) by SEQM_3:15
.= (((h ^\ n) . k) + ((c ^\ n) . k)) - ((c ^\ n) . k) by SEQ_1:7
.= (h ^\ n) . k ;
hence ((SVF1 (2,f,z0)) . (((h + c) ^\ n) . k)) - ((SVF1 (2,f,z0)) . ((c ^\ n) . k)) = (L . ((h ^\ n) . k)) + (R . ((h ^\ n) . k)) by A23, A8, A40, A41; :: thesis:

end;

A42: R is total by FDIFF_1:def 2;

now :: thesis:

let k be Element of NAT ; :: thesis:
thus (((SVF1 (2,f,z0)) /* ((h + c) ^\ n)) - ((SVF1 (2,f,z0)) /* (c ^\ n))) . k = (((SVF1 (2,f,z0)) /* ((h + c) ^\ n)) . k) - (((SVF1 (2,f,z0)) /* (c ^\ n)) . k) by RFUNCT_2:1
.= ((SVF1 (2,f,z0)) . (((h + c) ^\ n) . k)) - (((SVF1 (2,f,z0)) /* (c ^\ n)) . k) by A37, FUNCT_2:108
.= ((SVF1 (2,f,z0)) . (((h + c) ^\ n) . k)) - ((SVF1 (2,f,z0)) . ((c ^\ n) . k)) by A24, FUNCT_2:108
.= (L . ((h ^\ n) . k)) + (R . ((h ^\ n) . k)) by A39
.= ((L /* (h ^\ n)) . k) + (R . ((h ^\ n) . k)) by A26, FUNCT_2:115
.= ((L /* (h ^\ n)) . k) + ((R /* (h ^\ n)) . k) by A42, FUNCT_2:115
.= ((L /* (h ^\ n)) + (R /* (h ^\ n))) . k by SEQ_1:7 ; :: thesis:

end;

then ((SVF1 (2,f,z0)) /* ((h + c) ^\ n)) - ((SVF1 (2,f,z0)) /* (c ^\ n)) = (L /* (h ^\ n)) + (R /* (h ^\ n)) by FUNCT_2:63;
then A43: ((L /* (h ^\ n)) + (R /* (h ^\ n))) (#) ((h ^\ n) ") = ((((SVF1 (2,f,z0)) /* (h + c)) ^\ n) - ((SVF1 (2,f,z0)) /* (c ^\ n))) (#) ((h ^\ n) ") by A38, VALUED_0:27
.= ((((SVF1 (2,f,z0)) /* (h + c)) ^\ n) - (((SVF1 (2,f,z0)) /* c) ^\ n)) (#) ((h ^\ n) ") by A15, VALUED_0:27
.= ((((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c)) ^\ n) (#) ((h ^\ n) ") by SEQM_3:17
.= ((((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c)) ^\ n) (#) ((h ") ^\ n) by SEQM_3:18
.= ((((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c)) (#) (h ")) ^\ n by SEQM_3:19 ;
then A44: L . 1 = lim ((h ") (#) (((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c))) by A27, SEQ_4:22;
thus (h ") (#) (((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c)) is convergent by A27, A43, SEQ_4:21; :: thesis:
for y being Real st y in N2 holds
((SVF1 (2,f,z0)) . y) - ((SVF1 (2,f,z0)) . y0) = (L . (y - y0)) + (R . (y - y0)) by A23, A8;
hence partdiff (f,z0,2) = lim ((h ") (#) (((SVF1 (2,f,z0)) /* (h + c)) - ((SVF1 (2,f,z0)) /* c))) by A1, A3, A9, A44, Th12; :: thesis: