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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
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1 Answer

up vote 1 down vote accepted

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 $b\in B$?

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ab=f(a)b, right? Thanks! Damn it. can't believe I forgot this. –  user6495 Apr 29 '11 at 23:06
    
@user 6495: Exactly right. Don't worry, happens to all of us :) –  Zev Chonoles Apr 29 '11 at 23:07
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