How to convert a Polynomial Integer into String

I am trying to write the following (tex expression of)
variable df into a text file.

(20) -> df :=D(exp(x) + 2*x,x);
(20) ->
                                                    
Type: Expression Integer
(21) -> df
(21) ->
$$
{e \sp x}+2
\leqno(21)
$$

                                                    
Type: Expression Integer


I could use the command File(Expression Integer) as
described in 
section 9.24 of the Axiom book. 

Alternatively, I am trying to use the command TextFile
:

f1: TextFile := open("df.txt", "output");

writeLine!(f1,df);

close! f1;


But I get an error complaining  the second parameter
 in writeLine!(*,*)
should be of type String.
How to convert df into a String ?


Thanks advance for any assistance!

I am using  version axiom-mar2008.


Shin

Home page : http://www.lombok.demon.co.uk/



      __________________________________________________________
Sent from Yahoo! Mail.
A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html