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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:
 def start(self):
 		"""Get the start key of the first range. 		None if RangeMap is empty or unbounded to the left. 		"""

		if self._values[0] is NOT_SET:
			try:
				return self._keys[1]
			except IndexError:
				# This is empty or everything is mapped to a single value
				return None
		else:
			# This is unbounded to the left
			return self._keys[0]