lets
` <*>
  + <*>
  | + pure (\u1 -> (\u2 -> Term u1))
  | ` <|>
  |   + <*>
  |   | + pure (\u1 -> 'a')
  |   | ` satisfy
  |   ` <*>
  |     + pure (\u1 -> 'b')
  |     ` satisfy
  ` satisfy