(examples-for all?
  ("true when all items are numeric"
   (all? num? '(1 2 3 4))
   t)

  ("false when all items are not numeric"
   (all? num? '(1 2 x 4))
   nil)

  ("true for an atom"
   (and (all? string? "really, all") t)
   t)

  ("false for nil"
   (all? x1 nil)
   nil)

  ("false when any item is nil"
   (and (all? x1 '(1 2 nil 4)) t)
   nil))