let Z be open Subset of REAL; :: thesis: ( not 0 in Z & Z c= dom (ln * ((id Z) ^)) implies ( ln * ((id Z) ^) is_differentiable_on Z & ( for x being Real st x in Z holds
((ln * ((id Z) ^)) `| Z) . x = - (1 / x) ) ) )
set f = id Z;
assume that
A1: not 0 in Z and
A2: Z c= dom (ln * ((id Z) ^)) ; :: thesis: ( ln * ((id Z) ^) is_differentiable_on Z & ( for x being Real st x in Z holds
((ln * ((id Z) ^)) `| Z) . x = - (1 / x) ) )
dom (ln * ((id Z) ^)) c= dom ((id Z) ^) by RELAT_1:25;
then A3: Z c= dom ((id Z) ^) by A2, XBOOLE_1:1;
A4: for x being Real st x in Z holds
((id Z) ^) . x > 0
proof
let x be Real; :: thesis: ( x in Z implies ((id Z) ^) . x > 0 )
assume A5: x in Z ; :: thesis: ((id Z) ^) . x > 0
then A6: ((id Z) ^) . x = ((id Z) . x) " by A3, RFUNCT_1:def 2
.= 1 / x by A5, FUNCT_1:18 ;
((id Z) ^) . x in right_open_halfline 0 by A2, A5, FUNCT_1:11, TAYLOR_1:18;
then ex g being Real st
( 1 / x = g & 0 < g ) by A6, Lm1;
hence ((id Z) ^) . x > 0 by A6; :: thesis: verum
end;
A7: for x being Real st x in Z holds
(id Z) . x > 0
proof
let x be Real; :: thesis: ( x in Z implies (id Z) . x > 0 )
assume A8: x in Z ; :: thesis: (id Z) . x > 0
then ((id Z) ^) . x > 0 by A4;
then ((id Z) . x) " > 0 by A3, A8, RFUNCT_1:def 2;
hence (id Z) . x > 0 ; :: thesis: verum
end;
A9: (id Z) ^ is_differentiable_on Z by A1, FDIFF_5:4;
A10: for x being Real st x in Z holds
( ln * ((id Z) ^) is_differentiable_in x & diff ((ln * ((id Z) ^)),x) = (diff (((id Z) ^),x)) / (((id Z) ^) . x) )
proof
let x be Real; :: thesis: ( x in Z implies ( ln * ((id Z) ^) is_differentiable_in x & diff ((ln * ((id Z) ^)),x) = (diff (((id Z) ^),x)) / (((id Z) ^) . x) ) )
assume x in Z ; :: thesis: ( ln * ((id Z) ^) is_differentiable_in x & diff ((ln * ((id Z) ^)),x) = (diff (((id Z) ^),x)) / (((id Z) ^) . x) )
then ( (id Z) ^ is_differentiable_in x & ((id Z) ^) . x > 0 ) by A4, A9, FDIFF_1:9;
hence ( ln * ((id Z) ^) is_differentiable_in x & diff ((ln * ((id Z) ^)),x) = (diff (((id Z) ^),x)) / (((id Z) ^) . x) ) by TAYLOR_1:20; :: thesis: verum
end;
then A11: for x being Real st x in Z holds
ln * ((id Z) ^) is_differentiable_in x ;
then A12: ln * ((id Z) ^) is_differentiable_on Z by A2, FDIFF_1:9;
for x being Real st x in Z holds
((ln * ((id Z) ^)) `| Z) . x = - (1 / x)
proof
let x be Real; :: thesis: ( x in Z implies ((ln * ((id Z) ^)) `| Z) . x = - (1 / x) )
assume A13: x in Z ; :: thesis: ((ln * ((id Z) ^)) `| Z) . x = - (1 / x)
then (id Z) . x <> 0 by A7;
then A14: x <> 0 by A13, FUNCT_1:18;
diff ((ln * ((id Z) ^)),x) = (diff (((id Z) ^),x)) / (((id Z) ^) . x) by A10, A13
.= ((((id Z) ^) `| Z) . x) / (((id Z) ^) . x) by A9, A13, FDIFF_1:def 7
.= ((((id Z) ^) `| Z) . x) / (((id Z) . x) ") by A3, A13, RFUNCT_1:def 2
.= ((((id Z) ^) `| Z) . x) / (1 * (x ")) by A13, FUNCT_1:18
.= (- (1 / (x ^2))) / (1 * (x ")) by A1, A13, FDIFF_5:4
.= - (x / (x ^2))
.= - ((x / x) / x) by XCMPLX_1:78
.= - (1 / x) by A14, XCMPLX_1:60 ;
hence ((ln * ((id Z) ^)) `| Z) . x = - (1 / x) by A12, A13, FDIFF_1:def 7; :: thesis: verum
end;
hence ( ln * ((id Z) ^) is_differentiable_on Z & ( for x being Real st x in Z holds
((ln * ((id Z) ^)) `| Z) . x = - (1 / x) ) ) by A2, A11, FDIFF_1:9; :: thesis: verum