while True:
			pair = self.pop()
			if pair[0] == None:
				break
			pairs += pair,
		last_pair = self.__bottom
		for pair in pairs:
			if last_pair in self.__pairs and pair[0] <= self.__pairs[last_pair] and pair[1] > self.__pairs[last_pair]:
				self.__pairs[last_pair] = pair[1]
				del(self.__pairs[pair[0]])
			if last_pair in self.__pairs and pair[0] <= self.__pairs[last_pair]:
				if pair[1] > self.__pairs[last_pair]:
					self.__pairs[last_pair] = pair[1]
					del(self.__pairs[pair[0]])
			else:
				last_pair = pair[0]
		self.clear()

	def rewind(self):
		'''Reinitialises internal ordered list of ranges.'''
		self.__walk_list = list(self.__pairs.keys())

			elif end == None or this[1] > end:
				end = this[1]
		self.clear()
		return(end)

	def __len__(self):
		return(len(self.__pairs))

	def max(self):
		result = None
		for last in self.__pairs.itervalues():
			if result == None or result < last:
				result = last
		return(result)