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Function Proof

  • Thread starter andmcg
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  • #1
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Suppose that f composed with g equals g composed with f for all functions g. Show that f is the identity function.

I really just don't know where to start.
 

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  • #2
Fredrik
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*Deleted*

That was probably a bad tip. I'll try to think of something better.

OK, here we go...

If f isn't the identity, there's an x such that f(x)≠x. Now choose a g that contradicts that.
 
Last edited:

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