Question on HtDP

["Jeff Stephens" <jsteve17@tampabay.rr.com>]

I am attempting to learn Scheme using HtDP.  I reached node24 where I
encountered the "symbol=?" construct.  HtDP says,

"Scheme provides only one basic operation on symbols: symbol=?, a comparison
operation."

I note that using this construct in DrScheme works fine; however, trying to
use it with
mzscheme produces an error unless one first executes:

(require (lib "etc.ss"))

I found this out by searching for "symbol=?" in the DrScheme Help Desk,
where the only
references produced were in the docs for "Beginning, Intermediate, Advanced"
Student and
in MzLib.  There was no reference found in the R5RS doc.

This brings up  the obvious question - Is HtDP incorrect in saying that
Scheme provides the
"symbol=?" construct since there is no reference to this in R5RS.

Regards,
Jeff Stephens