The case of 12 persons on 55 occasions is solved thus:--

1 2 3 12 4 11 5 10 6 9 7 8

1 2 4 11 6 9 8 7 10 5 12 3

1 2 5 10 8 7 11 4 3 12 6 9

1 2 6 9 10 5 3 12 7 8 11 4

1 2 7 8 12 3 6 9 11 4 5 10

Here 1 is a repeater, and the cycle is 2, 3, 4, 5,... 12. We thus get 5

groups of 11 lines each.