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禁止使用这些文件复制、制造、销售或分发Keychron键鼠产品及高度相似产品，禁止将Keychron商标用于自身品牌
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For black pieces, the PST is accessed via a mirror table (sq@mirror@N) that flips the board vertically, so the same white-perspective tables work for both sides.
if (key is null)