For deme U, the population count was 1297 until a change 5634.42 generations ago, where it changed to 2004, remaining steady thereafter.
time_units: generations
demes:
  - name: U
    start_time: .inf
    epochs:
      - start_size: 1297
        end_time: 5634.42
      - start_size: 2004
        end_time: 0