A commutator is a basic group-theoretic operation, usually written as [a,b] = a⁻¹b⁻¹ab, measuring whether two elements commute. The paper uses it to encode NAND, XOR, and AND. commutator 是群论中的基本操作,通常写作 [a,b] = a⁻¹b⁻¹ab,用来衡量两个元素是否可交换。论文利用它来编码 NAND、XOR 和 AND。