| +--> 1. c
  | +--> 2. h
  | |--> 3. ab
  | +--> 3. h
  | +--> 4. c
  | |--> 1abdg
  | |--> 1c
  | |--> 1h
  | |--> 2ab
  | |--> 2c
  | |--> 2h
  | |--> 3ab
  | |--> 3c
  | |--> 3h
  | `--> 4c