Let \(f:A\to B\) be a surjective function. Define a relation on \(A\) by \[ a_0\sim a_1\quad\Longleftrightarrow\quad f(a_0)=f(a_1). \]
Show that \(\sim\) is an equivalence relation.
Let \(A^*\) be the set of equivalence classes. Show that there is a bijective correspondence between \(A^*\) and \(B\).