let a, b be Real; :: thesis: for Z being open Subset of REAL
for f, f1 being PartFunc of REAL ,REAL st Z c= dom ((id Z) - ((a + b) (#) f)) & f = ln * f1 & ( for x being Real st x in Z holds
( f1 . x = x + b & f1 . x > 0 ) ) holds
( (id Z) - ((a + b) (#) f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ) )
let Z be open Subset of REAL ; :: thesis: for f, f1 being PartFunc of REAL ,REAL st Z c= dom ((id Z) - ((a + b) (#) f)) & f = ln * f1 & ( for x being Real st x in Z holds
( f1 . x = x + b & f1 . x > 0 ) ) holds
( (id Z) - ((a + b) (#) f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ) )
let f, f1 be PartFunc of REAL ,REAL ; :: thesis: ( Z c= dom ((id Z) - ((a + b) (#) f)) & f = ln * f1 & ( for x being Real st x in Z holds
( f1 . x = x + b & f1 . x > 0 ) ) implies ( (id Z) - ((a + b) (#) f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ) ) )
assume A1: ( Z c= dom ((id Z) - ((a + b) (#) f)) & f = ln * f1 & ( for x being Real st x in Z holds
( f1 . x = x + b & f1 . x > 0 ) ) ) ; :: thesis: ( (id Z) - ((a + b) (#) f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ) )
then Z c= (dom (id Z)) /\ (dom ((a + b) (#) f)) by VALUED_1:12;
then A2: ( Z c= dom (id Z) & Z c= dom ((a + b) (#) f) ) by XBOOLE_1:18;
then A3: Z c= dom (ln * f1) by A1, VALUED_1:def 5;
A4: for x being Real st x in Z holds
(id Z) . x = (1 * x) + 0 by FUNCT_1:35;
then A5: ( id Z is_differentiable_on Z & ( for x being Real st x in Z holds
((id Z) `| Z) . x = 1 ) ) by A2, FDIFF_1:31;
A6: for x being Real st x in Z holds
( f1 . x = b + x & f1 . x > 0 ) by A1;
then A7: ( f is_differentiable_on Z & ( for x being Real st x in Z holds
(f `| Z) . x = 1 / (x + b) ) ) by A1, A3, Th1;
then A8: ( (a + b) (#) f is_differentiable_on Z & ( for x being Real st x in Z holds
(((a + b) (#) f) `| Z) . x = (a + b) * (diff f,x) ) ) by A2, FDIFF_1:28;
A9: for x being Real st x in Z holds
(((a + b) (#) f) `| Z) . x = (a + b) / (x + b)

proof

let x be Real; :: thesis: ( x in Z implies (((a + b) (#) f) `| Z) . x = (a + b) / (x + b) )
assume A10: x in Z ; :: thesis: (((a + b) (#) f) `| Z) . x = (a + b) / (x + b)
hence (((a + b) (#) f) `| Z) . x = (a + b) * (diff f,x) by A2, A7, FDIFF_1:28
.= (a + b) * ((f `| Z) . x) by A7, A10, FDIFF_1:def 8
.= (a + b) * (1 / (x + b)) by A1, A3, A6, A10, Th1
.= (a + b) / (x + b) by XCMPLX_1:100 ;
:: thesis: verum

end;

for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b)

proof

let x be Real; :: thesis: ( x in Z implies (((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) )
assume A11: x in Z ; :: thesis: (((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b)
then A12: ( f1 . x = x + b & f1 . x > 0 ) by A1;
(((id Z) - ((a + b) (#) f)) `| Z) . x = (diff (id Z),x) - (diff ((a + b) (#) f),x) by A1, A5, A8, A11, FDIFF_1:27
.= (((id Z) `| Z) . x) - (diff ((a + b) (#) f),x) by A5, A11, FDIFF_1:def 8
.= (((id Z) `| Z) . x) - ((((a + b) (#) f) `| Z) . x) by A8, A11, FDIFF_1:def 8
.= 1 - ((((a + b) (#) f) `| Z) . x) by A2, A4, A11, FDIFF_1:31
.= 1 - ((a + b) / (x + b)) by A9, A11
.= ((1 * (x + b)) - (a + b)) / (x + b) by A12, XCMPLX_1:128
.= (x - a) / (x + b) ;
hence (((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ; :: thesis: verum

end;

hence ( (id Z) - ((a + b) (#) f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((id Z) - ((a + b) (#) f)) `| Z) . x = (x - a) / (x + b) ) ) by A1, A5, A8, FDIFF_1:27; :: thesis: verum