Let $f : X \to Y$ be an invertible function. Show that $f$ has unique inverse.

Question

(Hint: suppose  $g_1$and  $g_2$ are two inverses of $f$. Then for all $y \in Y$, $fog_1(y) = 1 _Y (y) = fog_2 (y).$   Use ono-one ness of $f$)