(1 2 3 4 5 6):
  (1 2 3) (4 5 6)  d=9
  (1 2 4) (3 5 6)  d=7
  (1 2 5) (3 4 6)  d=5
  (1 2 6) (3 4 5)  d=3
  (1 3 4) (2 5 6)  d=5
  (1 3 5) (2 4 6)  d=3
  (1 3 6) (2 4 5)  d=1  <--
  (1 4 5) (2 3 6)  d=1  <-- solutions
  (1 4 6) (2 3 5)  d=1  <--
  (1 5 6) (2 3 4)  d=3