; Bel in Bel. 9 October 2019, 9:14 GMT


(def no (x)
  (id x nil))

(def atom (x)
  (no (id (type x) 'pair)))

(def all (f xs)
  (if (no xs)      t
      (f (car xs)) (all f (cdr xs))
                   nil))

(def some (f xs)
  (if (no xs)      nil
      (f (car xs)) xs
                   (some f (cdr xs))))

(def reduce (f xs)
  (if (no (cdr xs))
      (car xs)
      (f (car xs) (reduce f (cdr xs)))))