The population of deme B held at 4555 until 6383.1568 generations back, when it changed reaching 7791, which has been constant since then.
time_units: generations
demes:
  - name: B
    start_time: .inf
    epochs:
      - start_size: 4555
        end_time: 6383.1568
      - start_size: 7791
        end_time: 0