Erratum.
In the Research News article "Tournament competition fuels computer chess" (29 June, p. 1396), the figure was reprodeced incorrectly. Black has a third pawn on the black square immediately in front of the black king. The figure and its legend are reproduced herewith. One limitation offull-width search methods in computer chess is called the horizon effect. A human easily sees that white, although it has one less pawn, can win the game by advancing its leftmost pawn across the board, whereupon it is promoted, by the rules of chess, to a queen. The computer, if it does not search enough moves into the future, will not see this outcome and will be excessively concerned about black's apparent material advantage. [Drawing by Eleanor Warner] [See figure in the PDF file].