def __init__(self, chronology):
self._chronology = chronology<EOL>self._now = <NUM_LIT:0><EOL>self._next = six.advance_iterator(self._chronology)<EOL>
The chronology is a generator that updates the world.

        Yield how many seconds of fake time elapse. Think of each yield as a
        "sleep". We read the very first value immediately, so that the world can be
        initialized in the chronology.

        Args:
          chronology: a generator that updates the state of the world and then
          sleeps via yielding.