code: def previous(self):
  		
  		if self.index - 1 >= 0:					# more main line?
  			self.index = self.index - 1
  		elif self.stack:						# were we in a variation?
  			self.gametree = self.stack.pop()
  			self.index = len(self.gametree) - 1
  		else:
  			raise GameTreeEndError
  		self.node = self.gametree[self.index]
  		self.nodenum = self.nodenum - 1
  		self._setChildren()
  		self._setFlags()
  		return self.node
docs: Moves the 'Cursor' to & returns the previous 'Node'. Raises
  			'GameTreeEndError' if the start of a branch is exceeded.