Lim system

The Lim system is a Swiss pairing method: it organises players by score and produces opponents for the next round without using a full round robin. Its most recognisable feature is the order in which it handles scoregroups.

Players with the same score form a scoregroup. Lim defines the median scoregroup as the group whose score equals half the number of rounds already played. Pairing begins with the highest scoregroup and works downward until just before the median; it then begins with the lowest group and works upward. The median scoregroup is paired last.

Within a group, players are ordered by pairing number and the top half is tentatively paired with the bottom half. If a proposed pair would repeat an opponent or create a colour problem, the system uses exchanges or moves players, called floaters, to a neighbouring scoregroup. It tracks colour difference and colour preference to seek reasonable colour allocation while respecting its pairing restrictions.