eql
Major Section: PROGRAMMING
(remove x l) is l if x is not a member of l, else is the
result of removing all occurrences of x from l.
The guard for (remove x l) requires l to be a true list and
moreover, either x is eqlablep or all elements of l are
eqlablep.
Remove is a Common Lisp function. See any Common Lisp
documentation for more information. Note that we do not allow
keyword arguments (such as test) in ACL2 functions, in
particular, in remove.