const NULL_REDUCTION = 2;

    const king = switch (gs.side) {
        .white => @intCast(SquareType, @ctz(@bitCast(BoardType, gs.bitboards[@enumToInt(Chess.PE.K)]))),
        .black => @intCast(SquareType, @ctz(@bitCast(BoardType, gs.bitboards[@enumToInt(Chess.PE.k)]))),
    };
    var in_check = gs.isSquareAttacked(king, gs.side.enemy());

    const in_check = gs.inCheck();

    // NULL move pruning
    {
        if (depth >= 3 and !in_check and gs.ply != 0) {
            // backup board state
            var bck: GameState = undefined;
            gs.backup(&bck);
            // prepare GameState
            gs.side = gs.side.enemy();
            gs.enpassant = null;
            const s = -try negamax(gs, -beta, -beta + 1, depth - 1 - NULL_REDUCTION);
            gs.restore(&bck);
            if (s >= beta) {
                return beta;
            }
        }
    }

    - [NULL move pruning](https://web.archive.org/web/20071031095933/http://www.brucemo.com/compchess/programming/nullmove.htm)
      - TODO: see comment below the [video](https://www.youtube.com/watch?v=n6xAzopULxU&list=PLmN0neTso3Jxh8ZIylk74JpwfiWNI76Cs&index=63), this is not a perfect solution