I need to use a symbol like this |---| with a continuous line between the two vertical ones
You can join \vdash
and \dashv
:
\documentclass{article}
\newcommand{\vdashv}{\vdash\joinrel\dashv}
\begin{document}
$A \vdashv B$
\end{document}
If you need a shorter symbol,
\documentclass{article}
\newcommand{\vdashv}{%
\vdash\mathrel{\mkern-9mu}\dashv
}
\begin{document}
$A \vdashv B$
\end{document}
This is the maximum amount of backing up. With \joinrel
it is -3mu.
A different realization with shorter vertical bars:
\documentclass{article}
\usepackage{stmaryrd}
\newcommand{\connection}{\mapstochar\relbar\mapsfromchar}
\begin{document}
$A \connection B$
\end{document}
I am not totally serious...
\documentclass{standalone}
\usepackage{rotating}
\begin{document}
\rotatebox[origin=c]{180}{$\dashv$}$\!\dashv$
\end{document}
Not so good as an image export
Better in Adobe Reader
No luck in Detexify
Update
\reflectbox
(mirroring a symbol) from the graphicx
package does a better job.
\documentclass{standalone}
% \rotatebox
\usepackage{rotating}
% \reflectbox
\usepackage{graphicx}
\begin{document}
\texttt{\textbackslash rotatebox} \rotatebox[origin=c]{180}{$\dashv$}$\!\dashv$
\texttt{\textbackslash reflectbox} \reflectbox{$\dashv$}$\!\dashv$
\end{document}