anchor.diff:        return t'
       }
     | Univ n -> Success <| Univ (S n)
  -  | Prim (_, t) -> Success t
  +  | Postulated (_, t) -> Success t
  
positive.code:       return result
      }
    | Univ n -> Success <| Univ n
    | Prim (str, tp) -> Success <| Prim (str, tp)
  
  and apply (globals : Global.env) (t1 : term) (t2 : term) : term result =
    match t1 with
  
negative.code:         return App (t1', t2')
        }
      | Univ n -> Success <| Univ n
      | Postulated (str, tp) -> Success <| Postulated (str, tp)
  
  
  let equiv (globals : Global.env) t1 t2 : unit result =
  