code: def trace(self, n):
          "Restore the position in the history of individual v's nodes"
          trace_map = {}
          self._trace(n, trace_map)
          s = list(trace_map.keys())
          s.sort()
          return f trace(self, n):
          "Restore the position in the history of individual v's nodes"
          trace_map = {}
          self._trace(n, trace_map)
          s = list(trace_map.keys())
          s.sort()
          return s
docs: Restore the position in the history of individual v's nodes