Suppose that n divides m and that a is an idempotent of Zn
Chapter 15, Problem 54E(choose chapter or problem)
Suppose that n divides m and that a is an idempotent of Zn (that is, a2 = a). Show that the mapping x ?ax is a ring homomorphism from Zm to Zn. Show that the same correspondence need not yield a ring homomorphism if n does not divide m.
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