If it is finite and nonempty, then it must contain at least one idempotent. 如果它是有限和非空的，则它必须包含至少一个幂等元。
This paper is a study on the invertibility of the commutator of scalar-idempotent elements and scalar-involutory elements of a unitary ring. 摘要本文研究在一个有单位元的环中两个倍幂等元的换位子与两个倍对合元的换位子的可逆性问题。
