If a challenge decreases a handicap, then not only is the handicap above the victorious program decreased, but the handicap below it is increased unless such an increase would violate an established bound. Similarly, increasing the handicap to a lower program via a challenge also decreases the handicap to the program above, unless a bound would be violated. The motivation for this rule is so that if programs A and B have established that A is 3.5 stones above B, and program C beats B, then as C decreases the handicap to A the net handicap from A to B remains 3.5. Challenges are played on the IGS at the convenience of the participants. When possible, challenge games are announced in advance on the computer go mailing list.
Challenges are single games played at the handicap that the challenger is trying to establish.
If the current difference is 0 stones, then the game is played with a 5.5 komi and the defender having the choice of colors. Otherwise, the higher program plays white at the appropriate number of stones with 0.5 komi. Time controls Every participant in the ladder has a noted preferred time control setting for challenge games. The actual time controls used in a challenge game are determined by examining the preferences of the participants and taking the most generous settings of each. There is no absolutely fair way to play matches between programs that use differing scoring systems.