time_units: generations
demes:
- name: A
  epochs:
  - {start_size: 1}
- name: B
  epochs:
  - {start_size: 1}
migrations:
- {rate: 0.01, source: A, dest: B}
- {rate: 0.01, source: B, dest: A, start_time: 10, end_time: 5}