(defun remove* (symbol tree)
    "Removes SYMB0L from TREE."
    (cond
        ((null tree)
            tree)
        ((atom (car tree))
            (if
                (equalp symbol (car tree))
                (remove* symbol (cdr tree))
                (cons (car tree) (remove* symbol (cdr tree)))))
        (t
            (cons
                (remove* symbol (car tree))
                (remove* symbol (cdr tree))))))