anchor.diff:        return t'
       }
     | Univ n -> Success <| Univ (S n)
  -  | Prim (_, t) -> Success t
  +  | Postulated (_, t) -> Success t
  
positive.code:         return App (t1', t2')
        }
      | Univ n -> Success <| Univ n
      | Prim (str, tp) -> Success <| Prim (str, tp)
  
  
  let equiv (globals : Global.env) t1 t2 : unit result =
  
negative.code:   | Lambda (x, tp, tm) -> Lambda (x, shiftUp cutoff tp, shiftUp (S cutoff) tm)
    | App (t1, t2) -> App (shiftUp cutoff t1, shiftUp cutoff t2)
    | Univ n -> Univ n
    | Postulated (str, tp) -> Postulated (str, tp)
  
  
  
  