Lam 1999, p. 117, Ex 40B. Lam, Tsit-Yuen (1999), Lectures on modules and rings, Graduate Texts in Mathematics No. 189, Berlin, New York: Springer-Verlag, ISBN978-0-387-98428-5, MR1653294
Lam 1999, p. 85. Lam, Tsit-Yuen (1999), Lectures on modules and rings, Graduate Texts in Mathematics No. 189, Berlin, New York: Springer-Verlag, ISBN978-0-387-98428-5, MR1653294
Lam 1999, p. 86. Lam, Tsit-Yuen (1999), Lectures on modules and rings, Graduate Texts in Mathematics No. 189, Berlin, New York: Springer-Verlag, ISBN978-0-387-98428-5, MR1653294