hash table question

[Daniel L. Weinreb <DLW@ALDERAAN.SCRC.Symbolics.COM>]

No, it doesn't always return true.  sxhash is an "equal" hash, returning
the same value for equal structures, even if they're not eq.  So the
idea is that it does a tree walk and computes its number out of what it
finds in the leaves.  Since you've changed a leaf and it is no longer
"equal" to what it used to be, it can have a new sxhash value, and
probably does.  This could have been spelled out in more detail in CLtL.