Surjective Functions

A Function is surjective when all elements of the co-domain are mapped to.

This is also called "Onto"

Formally:

or "For all elements $y$ in $\mathbb{Y}$, there exists an $x$ in $\mathbb{X}$ such that $f$ at $x$ is equal to $y$

Exercise

Show that if two functions $f$ and $g$ are Surjective so is $g \bullet f$. Show an example of where $g \bullet f$ is Surjective but $f$ is not.