docs: def literalize(self):
          """
          Return an expression where NOTs are only occurring as literals.
          Applied recursively to subexpressions.
          """
          if self.isliteral:
              return self
          args = tuple(arg.literalize() for arg in self.args)
          if all(arg is self.args[i] for i, arg in enumerate(args)):
              return self
  
          return self.__class__(*args)