Until 5678.0 generations ago, the population of deme F was 844. At that point, it changed to 8442, where it has stayed up to now.
time_units: generations
demes:
  - name: F
    start_time: .inf
    epochs:
      - start_size: 844
        end_time: 5678.0
      - start_size: 8442
        end_time: 0