description: Set migration source and dest using defaults.
time_units: generations
defaults:
  epoch: {start_size: 1}
  migration: {dest: deme1, source: deme0}

demes: [{name: deme0}, {name: deme1}]

migrations:
- {end_time: 1, rate: 1, start_time: 2}
- {end_time: 0, rate: 0.5, start_time: 1}