(def-all-ss #\: (compose ...) ~ (complement R) ~ no = (annotate 'mac (fn (_) `(= L ,_))) #\. (...) ! (L 'r))
(if hd (= tl (= (cdr tl) (cons o nil))) (= hd (= tl (cons o nil))))
(if hd (tl=:cdr.tl= (cons o nil)) (hd=:tl= (cons o nil)))