# Latex \in and \Z both cause Undefined Control Sequence error

My code looks like this:

\documentclass{article}
\usepackage{mathtools}
\usepackage{amssymb}
\usepackage[margin=0.5in]{geometry}
\setlength{\parindent}{0em}
\setlength{\parskip}{1em}

\begin{document}
...
Ex. If $x$ is even, then $x^2$ is even.
Proof: Let $y$ \in \Z $: x = 2y$ (we know y exists from the definition of even). Then:
$$x^2 = (2y)^2 x^2 = 4y^2 x^2 = 2(2y^2) (2y^2) is an Integer (because Integers are closed under multiplication), so x^2 is Even.$$


But when I run pdflatex file.tex, I get

! Undefined control sequence.
l.26 Proof: Let $y$ \in
\Z $: x = 2y$ (we know y exists from the defini...

?


I tried putting the \in \Z in the $...$ section, and tried changing $...$ to $$...$$, to no avail. What could be causing this and how can I fix it?

(To explain: I got the symbols from this list. It seems the list is not entirely accurate)

\end{document}


• Yes, that looks good too! Thank you (I upvoted your answer, but don't yet have enough rep for it to show). – Miryafa Aug 22 '16 at 20:12