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=Improving Chinook=
During his half year [https://en.wikipedia.org/wiki/Sabbatical sabbatical] in [[Maastricht University|Maastricht]] in early 1994 with the aim to prepare and improve his [[Checkers]] player [https://en.wikipedia.org/wiki/Chinook_(draughts_player) Chinook] for the 2nd upcoming [https://en.wikipedia.org/wiki/Marion_Tinsley Tinsley] match,
[[Jonathan Schaeffer]] worked along with Stef Keetman to profit from some of his ideas implemented in Truus. One of Truus' novel features was the extensive use of [[Tactics|tactical]] patterns in the [[Evaluation|evaluation]] function, and its ability to [[Learning|learn]] Draught Draughts tactics.
When Truus found a forced sequence of moves that won a checker, the program would remember the conditions necessary for the sequence to work. The so called two-for-one pattern, where a sacrifice of a checker due to the mandatory capture allows recapturing two or more checkers by successive jumps, was adapted to Chinook.
Many conditions and exceptions had to be considered which was quite error prone - therefore the possible inexact pattern match was not used in evaluation, but to trigger an [[Extensions|extension]], improving Chinook's strength considerably
