OpenStudy (anonymous):

If a function is surjective it has a right inverse. It seems like this can only be true if we grant ourselves the axiom of choice. Is this correct?

5 years ago
OpenStudy (anonymous):

Take a surjective function $$f : X \to Y$$. Since it is surjective we know that for any given $$y \in Y$$ there exists a non-empty preimage $$\{x; f(x) = y\}$$. So to construct a right inverse $$f^{-1} : Y \to X$$ such that $$f(f^{-1}(y)) = y$$ it would seem that for each of the preimages mentioned previously we would need to choose one element. Thus, we need the axiom of choice. Is that indeed true?

5 years ago
OpenStudy (anonymous):

Finally, are there any interesting consequences if we reject the axiom choice and lose the implied existence of right inverses for surjective functions?

5 years ago
OpenStudy (jhannybean):

@tcarroll010 perhaps?

5 years ago
OpenStudy (helder_edwin):

i don't remember much of my set theory lectures but AC is the centerpiece of ZFC. Mathematics without AC is very different. As u pointed out, there r lots of things that may seems trivial but depend deeply on AC.

5 years ago
OpenStudy (helder_edwin):

u could take a look at: "the axiom of choice" by Jech "Discovering Modern Set Theory" 2vols by Just and Weese

5 years ago
OpenStudy (anonymous):

I suppose it really takes a book to discuss the consequences of the axiom of choice.In any case, thanks.

5 years ago
OpenStudy (anonymous):

There are some very strange results like the Banach-Tarski paradox.

5 years ago
OpenStudy (helder_edwin):

u r welcome. i remember i loved my set theory lectures. some crazy things!

5 years ago