Код:
(defun _deepest (x i d)
(cond ((null x) d)
((atom x) (if (> i (car d)) (list i x) d))
(T (_deepest (cdr x) i (_deepest (car x) (+ i 1) d)))))
(defun deepest (x)
(cadr (_deepest x 0 (list 0 nil))))
(deepest '((1) 5 ((8) 9 (4)))) -> 8
(deepest '((1) 5 ((8 3) 9 (4)) 2)) -> 8
(deepest '(1)) -> 1