latex union code example

Example 1: union latex

$\cup$ gives you the union symbol
$\cap$ gives you the intersection symbol

Example 2: union of n elements latex

$\bigcup\limits_{i=1}^{\infty} F_{i}$

Example 3: latex x element of symbol

\documentclass{article}
\usepackage{graphicx}
\usepackage{amsmath}

\newcommand\Inn{%
  \mathrel{\ooalign{$\subset$\cr\hfil\scalebox{0.8}[1]{$=$}\hfil\cr}}%
}
\begin{document}

\[
A\in B % one stroke in middle
\]

\[
A\Inn B % two strokes in middle
\]

\end{document}