- #1
Bashyboy
- 1,421
- 5
Homework Statement
##f : A \rightarrow B## if and only if ##\exists g : B \rightarrow A## with the property ##(g \circ f)(a) = a##, for all ##a \in A## (In other words, ##g## is the left inverse of ##f##)
Homework Equations
The Attempt at a Solution
I have already prove the one direction. Now I am trying to verify that, if ##f## is injective, then there must exist a left inverse ##g##. However, I am having great difficulty in doing so. I am understand the philosophy behind it: I have to define a function ##g## so that ##(g \circ f)(a) = a## holds true. But I cannot see how to explicitly use f's injectivity to construct such a function. Would someone mind pointing me in the right direction?