time_units: generations
demes:
- name: A
  epochs:
    - start_size: 1000
- name: B
  epochs:
    - start_size: 1000
- name: C
  start_time: 100
  ancestors: [B]
  epochs:
    - start_size: 1000
migrations:
- demes: [A, B, C]
  rate: 1e-5