From: Steve Knight
Subject: Re: Weak Reference in Common Lisp
Date: Thu, 23 Aug 1990 10:05:25 +0000
Message-ID: <1350027@otter.hpl.hp.com>

>> Some Common Lisp implementations ...  If the only reference to an object 
>> is as the key in such a hash table it may be removed from the hash table
>> (along with the value) and may then be GCed.

> You *have* to mention that that would only be reasonable for EQ hash tables.
> Not for EQUAL hash tables, or any other predicate you can think of.

99.9% true.  You can use EQUAL "temporary" hash-tables to implement
uniquely allocated datatypes (ie. values for which EQ implies EQUAL).

Steve