Rassoc is a Common Lisp function. See any Common Lisp
documentation for more information.
eql as test
Major Section: PROGRAMMING
(Rassoc x alist) is similar to (assoc x alist), the difference
being that it looks for the first pair in the given alist whose
cdr, rather than car, is eql to x. See assoc.
The guard of rassoc requires its second argument to be an alist,
and in addition, that either its first argument is eqlablep or
else all second components of pairs belonging to the second argument
are eqlablep. See eqlablep.
Rassoc is a Common Lisp function. See any Common Lisp
documentation for more information.