[plt-scheme] using syntax objects as hash table keys

ifconfig nslookup writes:
 > Why do you want to do that?

Not sure how it's relevant to the question, but I'll tell anyway:

I want to determine whether an expression implies the other, for example
#'(integer? x) implies #'(number? x).  I can assert that #'integer?
implies #'number?, but when I query those assertions, I need to make
sure the identifier in the expression refers to the same binding as
the one in the assertion.  And in order to make the query efficient,
it would help to use a hash table instead of an alist.

--dougo at place.org