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==The SEX Horizon Effect==
When looking for a deep combination the program would sometimes terminate the true [[Principal variationVariation|principal variation]] prematurely as a result of examining uninteresting moves for the defending side. These uninteresting moves would cause big values of SXDEC which would often wipe out all the remaining SX needed by the program to prove the soundness of the combination.
We overcome this problem in the SEX algorithm by using two separate values of SEX, one for each side. If the value of SEX for either side (or for both sides) remains positive then the search continues. This means that a combination will be found even of the defending side makes uninteresting moves, because the attacking side will score a series of low values for SEXDEC. This change produced a clear improvement in the performance of the program.
