lets
+ let <hidden>
| ` <|>
|   + <*>
|   | + <*>
|   | | + pure (\u1 -> (\u2 -> (\u3 -> u1 : u2 u3)))
|   | | ` satisfy
|   | ` rec <hidden>
|   ` pure (\u1 -> u1)
` <*>
  + <*>
  | + pure (\u1 -> (\u2 -> Term (u1 Term)))
  | ` ref <hidden>
  ` eof