Get rules at specific position in the structure.
        :param x: X coordinate
        :param y: Y coordinate
        :return: List of rules

def rules(self, x, y):
        # type: (int, int) -> List[Type[Rule]]
        """
        Get rules at specific position in the structure.
        :param x: X coordinate
        :param y: Y coordinate
        :return: List of rules
        """
        return [r for r in self._field[y][x]]