(defun all-subsequences2 (list)
  (labels ((recurse (s list)
             (if (endp list)
                 (if (>= s 3)
                     '(())
                     '())
                 (let ((x (car list))
                       (xs (cdr list)))
                   (if (evenp s)
                       (append (mapcar (lambda (ys) (cons x ys))
                                       (recurse (+ s 1) xs))
                               (recurse s xs))
                       (append (mapcar (lambda (ys) (cons x ys))
                                       (recurse s xs))
                               (recurse (+ s 1) xs)))))))
    (recurse 0 list)))