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9.6.5 Null move

Fruit uses R=3 recursive null move, even in the endgame.

In Fruit, a precondition to using null move is that the static eval fails high. One of the consequences of this is that no two null moves can be played in a row (this is because the evaluation is symmetrical). This is a usual condition but notice that in Fruit the null-move condition is "pure" (independent of move paths). The fail-high condition was selected for other reasons however.

Also, a verification search is launched in the endgame.