let Z be open Subset of REAL; :: thesis: ( Z c= dom (exp_R * tan) implies ( exp_R * tan is_differentiable_on Z & ( for x being Real st x in Z holds
((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2) ) ) )
assume A1: Z c= dom (exp_R * tan) ; :: thesis: ( exp_R * tan is_differentiable_on Z & ( for x being Real st x in Z holds
((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2) ) )
A2: for x being Real st x in Z holds
cos . x <> 0

proof

let x be Real; :: thesis: ( x in Z implies cos . x <> 0 )
assume x in Z ; :: thesis: cos . x <> 0
then x in dom (sin / cos) by A1, FUNCT_1:11;
hence cos . x <> 0 by Th1; :: thesis: verum

end;

A3: for x being Real st x in Z holds
exp_R * tan is_differentiable_in x

proof

let x be Real; :: thesis: ( x in Z implies exp_R * tan is_differentiable_in x )
assume x in Z ; :: thesis: exp_R * tan is_differentiable_in x
then cos . x <> 0 by A2;
then A4: tan is_differentiable_in x by FDIFF_7:46;
exp_R is_differentiable_in tan . x by SIN_COS:65;
hence exp_R * tan is_differentiable_in x by A4, FDIFF_2:13; :: thesis: verum

end;

then A5: exp_R * tan is_differentiable_on Z by A1, FDIFF_1:9;
for x being Real st x in Z holds
((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2)

proof

let x be Real; :: thesis: ( x in Z implies ((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2) )
A6: exp_R is_differentiable_in tan . x by SIN_COS:65;
assume A7: x in Z ; :: thesis: ((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2)
then A8: cos . x <> 0 by A2;
then tan is_differentiable_in x by FDIFF_7:46;
then diff ((exp_R * tan),x) = (diff (exp_R,(tan . x))) * (diff (tan,x)) by A6, FDIFF_2:13
.= (diff (exp_R,(tan . x))) * (1 / ((cos . x) ^2)) by A8, FDIFF_7:46
.= (exp_R . (tan . x)) / ((cos . x) ^2) by SIN_COS:65 ;
hence ((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2) by A5, A7, FDIFF_1:def 7; :: thesis: verum

end;

hence ( exp_R * tan is_differentiable_on Z & ( for x being Real st x in Z holds
((exp_R * tan) `| Z) . x = (exp_R . (tan . x)) / ((cos . x) ^2) ) ) by A1, A3, FDIFF_1:9; :: thesis: verum