Grillet, Pierre Antoine, Abstract Algebra, Graduate Texts in Mathematics 242, Springer, Lemma 9.2, p. 183, 2007 [2016-07-08], ISBN 9780387715681, (原始内容存档于2019-07-12).
Grillet, Pierre Antoine, Abstract Algebra, Graduate Texts in Mathematics 242, Springer, Lemma 9.2, p. 183, 2007 [2016-07-08], ISBN 9780387715681, (原始内容存档于2019-07-12).