Until 8851.0 generations ago, the population of deme D was 9903. At that point, it changed to 592, where it has stayed up to now.
time_units: generations
demes:
  - name: D
    start_time: .inf
    epochs:
      - start_size: 9903
        end_time: 8851.0
      - start_size: 592
        end_time: 0