



 
Brian, It isn't possible for every pair of players to play together. The best you can get is a schedule where no 2 players are together twice. That turns out to be possible. There is a nice schedule for 9 players that has every pair together exactly once over 4 days. It is this ABC DEF GHI, AHF DBI GEC, ADG BEH CFI, AEI BFG CDG. Randomly (or not so randomly) split your 18 into two groups of 9, and then use this schedule on each group. Have fun!  


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