let Z be open Subset of REAL ; :: thesis: ( Z c= dom tan & Z c= ].(- 1),1.[ implies ( tan (#) (arctan + arccot ) is_differentiable_on Z & ( for x being Real st x in Z holds
((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) ) ) )
assume that
A1: Z c= dom tan and
A2: Z c= ].(- 1),1.[ ; :: thesis: ( tan (#) (arctan + arccot ) is_differentiable_on Z & ( for x being Real st x in Z holds
((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) ) )
A3: arctan + arccot is_differentiable_on Z by A2, Th37;
for x being Real st x in Z holds
tan is_differentiable_in x

proof

let x be Real; :: thesis: ( x in Z implies tan is_differentiable_in x )
assume x in Z ; :: thesis: tan is_differentiable_in x
then cos . x <> 0 by A1, FDIFF_8:1;
hence tan is_differentiable_in x by FDIFF_7:46; :: thesis: verum

end;

then A4: tan is_differentiable_on Z by A1, FDIFF_1:16;
A5: ].(- 1),1.[ c= [.(- 1),1.] by XXREAL_1:25;
then ].(- 1),1.[ c= dom arccot by SIN_COS9:24, XBOOLE_1:1;
then A6: Z c= dom arccot by A2, XBOOLE_1:1;
].(- 1),1.[ c= dom arctan by A5, SIN_COS9:23, XBOOLE_1:1;
then Z c= dom arctan by A2, XBOOLE_1:1;
then Z c= (dom arctan ) /\ (dom arccot ) by A6, XBOOLE_1:19;
then A7: Z c= dom (arctan + arccot ) by VALUED_1:def 1;
then Z c= (dom tan ) /\ (dom (arctan + arccot )) by A1, XBOOLE_1:19;
then A8: Z c= dom (tan (#) (arctan + arccot )) by VALUED_1:def 4;
for x being Real st x in Z holds
((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 )

proof

let x be Real; :: thesis: ( x in Z implies ((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) )
assume A9: x in Z ; :: thesis: ((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 )
then A10: cos . x <> 0 by A1, FDIFF_8:1;
((tan (#) (arctan + arccot )) `| Z) . x = (((arctan + arccot ) . x) * (diff tan ,x)) + ((tan . x) * (diff (arctan + arccot ),x)) by A8, A4, A3, A9, FDIFF_1:29
.= (((arctan . x) + (arccot . x)) * (diff tan ,x)) + ((tan . x) * (diff (arctan + arccot ),x)) by A7, A9, VALUED_1:def 1
.= (((arctan . x) + (arccot . x)) * (1 / ((cos . x) ^2 ))) + ((tan . x) * (diff (arctan + arccot ),x)) by A10, FDIFF_7:46
.= (((arctan . x) + (arccot . x)) / ((cos . x) ^2 )) + ((tan . x) * (((arctan + arccot ) `| Z) . x)) by A3, A9, FDIFF_1:def 8
.= (((arctan . x) + (arccot . x)) / ((cos . x) ^2 )) + ((tan . x) * 0 ) by A2, A9, Th37
.= ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) ;
hence ((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) ; :: thesis: verum

end;

hence ( tan (#) (arctan + arccot ) is_differentiable_on Z & ( for x being Real st x in Z holds
((tan (#) (arctan + arccot )) `| Z) . x = ((arctan . x) + (arccot . x)) / ((cos . x) ^2 ) ) ) by A8, A4, A3, FDIFF_1:29; :: thesis: verum