docs: def cancel(self):
          """
          Cancel itself and following NOTs as far as possible.
          Returns the simplified expression.
          """
          expr = self
          while True:
              arg = expr.args[0]
              if not isinstance(arg, self.__class__):
                  return expr
              expr = arg.args[0]
              if not isinstance(expr, self.__class__):
                  return expr