# Function Proof

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.

Fredrik
Staff Emeritus
Gold Member
*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.

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