def is_valid(self):
        # noinspection PyUnresolvedReferences,PyUnusedLocal
        """Check if this state is a valid state.

        Returns
        -------
        bool :
            Whether the state is valid or not.

        Notes
        -----
        Optionally this method can be overwritten at runtime.

        Examples
        --------
        >>> def my_is_valid(self)
        ...     pass
        ...
        >>> MDPPrimitive.is_valid = my_is_valid

        """
        return True