let Z be open Subset of REAL; :: thesis: for f being PartFunc of REAL,REAL st Z c= dom ((1 / 2) (#) (arccot * f)) & ( for x being Real st x in Z holds
( f . x = 2 * x & f . x > - 1 & f . x < 1 ) ) holds
( (1 / 2) (#) (arccot * f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) ) )
let f be PartFunc of REAL,REAL; :: thesis: ( Z c= dom ((1 / 2) (#) (arccot * f)) & ( for x being Real st x in Z holds
( f . x = 2 * x & f . x > - 1 & f . x < 1 ) ) implies ( (1 / 2) (#) (arccot * f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) ) ) )
assume that
A1: Z c= dom ((1 / 2) (#) (arccot * f)) and
A2: for x being Real st x in Z holds
( f . x = 2 * x & f . x > - 1 & f . x < 1 ) ; :: thesis: ( (1 / 2) (#) (arccot * f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) ) )
A3: for x being Real st x in Z holds
( f . x = (2 * x) + 0 & f . x > - 1 & f . x < 1 ) by A2;
A4: Z c= dom (arccot * f) by A1, VALUED_1:def 5;
then A5: arccot * f is_differentiable_on Z by A3, Th88;
for x being Real st x in Z holds
(((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2)))

proof

let x be Real; :: thesis: ( x in Z implies (((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) )
assume A6: x in Z ; :: thesis: (((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2)))
then (((1 / 2) (#) (arccot * f)) `| Z) . x = (1 / 2) * (diff ((arccot * f),x)) by A1, A5, FDIFF_1:20
.= (1 / 2) * (((arccot * f) `| Z) . x) by A5, A6, FDIFF_1:def 7
.= (1 / 2) * (- (2 / (1 + (((2 * x) + 0) ^2)))) by A4, A3, A6, Th88
.= - (1 / (1 + ((2 * x) ^2))) ;
hence (((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) ; :: thesis: verum

end;

hence ( (1 / 2) (#) (arccot * f) is_differentiable_on Z & ( for x being Real st x in Z holds
(((1 / 2) (#) (arccot * f)) `| Z) . x = - (1 / (1 + ((2 * x) ^2))) ) ) by A1, A5, FDIFF_1:20; :: thesis: verum