Sen-ai-sen

Sen-ai-sen refers to a now largely historical handicap system in Go, where the weaker player takes Black in two out of every three games. The sequence follows the pattern: Black, White, Black. This form of handicap was considered the mildest available in professional play prior to the widespread introduction of komi.

The purpose of this system was to slightly balance the odds in matches between players of nearly equal strength, when a full handicap was deemed excessive.

The structure was most often used in series of games. After a fixed number of wins—typically three consecutive victories—the handicap would be adjusted, either reduced to tagaisen (even games) or increased to josen (permanent Black for the weaker player).