F deme's population was steady at 9993 before it changed to 1815 319.6 generations ago, maintaining that number to the present.
time_units: generations
demes:
  - name: F
    start_time: .inf
    epochs:
      - start_size: 9993
        end_time: 319.6
      - start_size: 1815
        end_time: 0