[plt-scheme] Is there an error in "convert.ss" teachpack

Working with HtDP exercise 2.2.1 I typed the following in the define window :

(define (f2c temp)
  (* 5/9 (- temp 32)))

This works fine by itself in the interactions window :

Welcome to DrScheme, version 205.6-cvs21nov2003.
Language: Beginning Student.
Teachpack: /usr/local/plt/teachpack/htdp/convert.ss.
> (f2c 88)
31.1

But, when I follow the instructions in the exercise I get the following error:

> (convert-gui f2c)
convert-gui: primitive operator convert-gui expects a defined procedure name 
(usually `f2c') in this position
> 

Regards,
Jeff Stephens