approach ko

An approach ko—also called a yose-ko—is a ko in which one side cannot recapture immediately. That player must first make an approach move that enables the recapture. The opponent may answer this approach move, so resolving the ko requires an extra move beyond the usual ko repetition.

This additional approach move changes the ko’s value and is particularly important when evaluating endgame sequences and move order. Unlike an ordinary ko, an approach ko is asymmetric: only one side needs the extra move before recapturing. It should not be identified merely because it arises during yose; the defining feature is the required approach move before recapture.