time_units: generations
defaults:
  migration: {end_time: 100}
demes:
- name: a
  epochs:
  - {start_size: 1}
- name: b
  epochs:
  - {start_size: 1}
- name: c
  epochs:
  - {start_size: 1}
- name: d
  epochs:
  - {start_size: 1}
migrations:
- {rate: 0.1, source: a, dest: b, start_time: 200}
- {rate: 0.1, source: a, dest: b, start_time: 100, end_time: 50}
- rate: 0.1
  demes: [c, d]
  start_time: 200
- rate: 0.1
  demes: [c, d]
  start_time: 100
  end_time: 50