\bar y polinomios

Question

Is it possible in Latex to get this expession ?.

I have tried like this

$\bar {\exists  Z }= \bar {\left \{ x_1x_2: \exists ix_i = 0 \right \}}  $

and only shows the bar over the exists symbol.

Answer 1

You should use \overline instead of \bar. While the length of the bar displayed with \bar is fixed, the length of the bar displayed with \overline varies according to its argument.

\documentclass{article}
\begin{document}
\( \overline{\{ x_1 x_2 : \exists i \ x_i = 0\}} \)
\end{document}

Also, there's no need to use \left and \right here since the curly brackets will not get any bigger.

Answer 2

Another approach could be using \widebar with a macro of @Hendrik Vogt Can I get a \widebar without using the mathabx package?. Here there is the result.

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools,amssymb}
\usepackage{braket}
\makeatletter % using \widebar macro Hendrik Vogt: https://tex.stackexchange.com/questions/16337/can-i-get-a-widebar-without-using-the-mathabx-package/60253#60253
\newcommand*\rel@kern[1]{\kern#1\dimexpr\macc@kerna}
\newcommand*\widebar[1]{%
  \begingroup
  \def\mathaccent##1##2{%
    \rel@kern{0.8}%
    \overline{\rel@kern{-0.8}\macc@nucleus\rel@kern{0.2}}%
    \rel@kern{-0.2}%
  }%
  \macc@depth\@ne
  \let\math@bgroup\@empty \let\math@egroup\macc@set@skewchar
  \mathsurround\z@ \frozen@everymath{\mathgroup\macc@group\relax}%
  \macc@set@skewchar\relax
  \let\mathaccentV\macc@nested@a
  \macc@nested@a\relax111{#1}%
  \endgroup
}
\makeatother
\begin{document}
\[\widebar{\Set{x_1 x_2 \colon \exists i \, x_i = 0}}\]
\end{document}

The \Set command is used with braket package to give a just blank spaces to the left and to the right.