(defun is-factor (n x)
        (cond
                ((eq (mod n x) 0) T)
                (T NIL)
        )
)

(defun prime-recurse (n x l)
        (cond
                ((is-factor n x) NIL)
                ((> x l) T)
                (T (prime-recurse n (1+ x) l) )
        )
)

(defun is-prime (n) (prime-recurse n 2 (sqrt n)))