time_units: generations
defaults:
  epoch: {start_size: 1}
demes:
- {name: A}
- {name: B}
- {name: C}
- {name: D}
migrations:
- {rate: 0.5, source: B, dest: A}
- {rate: 0.5, source: C, dest: A}
- {rate: 1e-03, source: D, dest: A}