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History leaf pruning is pruning based on history counters. The idea is to prune moves that are <= 0 depth after reductions and are below a given history threshold. History Leaf Pruning showed up as an option in Fruit 05/11/03 by Fabien Letouzey.

// example
if (node_type != NodePV) {
    if (!in_check && played_nb >= 5 && !extended) {
        value = sort->value; // history score
        if (value < HistoryThreshold) {
            new_depth -= 1;
            if (value < LeafThreshold) continue; // History Leaf pruning
            reduced = true;
        }
    }
}

See also

• Bobby's Strategic Quiescence Search
• Butterfly Boards
• Butterfly Heuristic
• Futility Pruning
• History Heuristic
• Late Move Reductions
• Reductions
• Relative History Heuristic

Forum Posts

• Re: Possible search improvment by Ryan Benitez, CCC, June 17, 2009 » ProbCut
• Can someone explain this? by Michel Van den Bergh, CCC, October 07, 2009 » Toga

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