Claim:Functions with left inverses are injective

From CS2800 wiki
If a function [math]f : A \href{/cs2800/wiki/index.php/%5Cto}{\to} B [/math] has a left inverse [math]g : B \href{/cs2800/wiki/index.php/%5Cto}{\to} A [/math], then [math]f [/math] is injective.