logical_not_expr: 'not' logical_not_expr
                        | comparison

def logical_not_expr(self):
        """
        logical_not_expr: 'not' logical_not_expr
                        | comparison
        """
        if self.token.nature == Nature.NOT:
            token = self.token
            self._process(Nature.NOT)
            return UnaryOperation(op=token, right=self.logical_not_expr())
        else:
            return self.comparison()