Recently I was wondering if we need the Axiom of Choice in order to find an inverse function given an bijective funcion:
If f:A→B is bijective we mean that f is injective and surjective. Assume that f:A→B is bijective. I want to define f−1:B→A s.t. f∘f−1=1B and f−1∘f=1A. For each b∈B let Xb:={x∈X:f(x)=b}. By surjectivity each Xb is non-empty. But not knowing wether A or B are finite I need AC in order to select from each Xb an (in fact unique) element xb and defining f−1(b):=xb for each b∈B.
Is AC necassary ?
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