# Exercise in Atiyah (localization)

Let me refer you to:

http://www-users.math.umd.edu/~karpuk/chap3solns.pdf

Page 2, ex. 4

Can you please explain the following step:

$tb=f(s')b=s'b$

Why $f(s')=s'$ ?

Thanks

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@user6495: That is a 16-page document. You need to be more specific about where. – Zev Chonoles Apr 29 '11 at 22:59
@Zev Chonoles: sorry, just edited it. – user6495 Apr 29 '11 at 23:00

Hint: We have a map $f:A\rightarrow B$. This makes $B$ into an $A$-module. What is the definition of "$ab$", for $a\in A$ and $b\in B$?