module Std

  let halt = any

  let fail { false } = any

  let if (b: bool) (then {b}) (else {not b}) = any

end

module List

  use list.List

  let unList < 'a > (l: list 'a)
    (onCons (h: 'a) (t: list 'a) {l = Cons h t})
    (onNil {l = Nil})
  = any

end