Seminario_TP3_EJ06

(defun mascara (l1 l2 &optional (l3 nil))
    (if (null l1) l3
        (if (= 0 (car l1))
            (mascara (cdr l1) (cdr l2) l3)
            (mascara (cdr l1) (cdr l2) (append l3 (list (car l2))))
        )
    )
)