SOLUTION: Consider the following statement: Let f be a function, such that for all a and b in the domain of f, f(a)=f(b) implies a=b. Then the function f has an inverse.
Is this stat
Under the given condition, we can define the function g on the set of the images {b | b = f(a), a belongs to A} in a way
g(b) = a, if f(a) = b.
This function is defined correctly on this set and is the inverse function to f.