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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def start(self) -> None: """Coroutine to run this server."""

        if self._is_running:
            raise SublemonRuntimeError(
                'Attempted to start an already-running `Sublemon` instance')

        self._poll_task = asyncio.ensure_future(self._poll())
        self._is_running = True