Pairing exchange

The Dutch system is a regulated method for creating pairings in Swiss tournaments, where a fixed number of rounds is played and players on similar scores generally meet. When it processes a bracket, meaning the set of players currently being paired, it temporarily divides that bracket into two subgroups called S1 and S2. Resident players are the players from the scoregroup that created the bracket, rather than players carried down from a higher one.

A pairing exchange changes subgroup membership. A set of residents from S1 is swapped with an equally sized set from S2. The subgroups are then ordered again and new candidate pairings are tested. This lets the algorithm reach combinations that were impossible while the original split remained intact.

This is not a change to a published round and not an agreement to switch opponents. It is an internal algorithmic step taken before the pairings are finalized. Exchanges are normally considered after pairing transpositions have been exhausted. A transposition changes the order inside S2 but does not move players from one subgroup to the other.