time_units: generations
defaults:
  pulse: {sources: [a]}
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}
pulses:
- {dest: b, proportions: [0.1], time: 100}
- {dest: c, proportions: [0.1], time: 100}
- {dest: d, proportions: [0.1], time: 100}
- {sources: [d], dest: a, proportions: [0.2], time: 200}