[racket] Possible typos in HtDP2e

>From a question on StackOverflow [1], it seems that on this page:
http://www.ccs.neu.edu/home/matthias/HtDP2e/part_4.html
 unsyntax `#,' appears 3 times, in places where it should probably not be.

Can someone confirm this or explain what this should mean?

Thanks,
Laurent

[1] http://stackoverflow.com/questions/19726343/in-maybe-letter/
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