What command to use for reversed $\vDash$?

Question

I want to use a symbol similar to

$\vDash$ 

but reversed (like if it's mirrored against an imaginary vertical line). I cannot find such a symbol anywhere. I have used detexify too but no luck there either.

Do you know what command and package I should use?

Answer 1

Constructed symbol

If the font does not provide the symbol, the mirroring can be done with package graphicx:

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

\makeatletter
\providecommand*{\Dashv}{%
  \mathrel{%
    \mathpalette\@Dashv\vDash
  }%
}
\newcommand*{\@Dashv}[2]{%
  \reflectbox{$\m@th#1#2$}%
}
\makeatother

\begin{document}
\[ A \vDash B \Dashv C \]
\end{document}

Remark:

• The stuff with \mathpalette ensures that the symbol is properly scaled if it is used in different contexts (as index, in fractions, …).

Font package MnSymbol

If package MnSymbol is loaded (it also changes other math symbols), then the symbol is available as \leftmodels:

\documentclass{article}
\usepackage{MnSymbol}
\begin{document}
\[ A \leftmodels B \]
\end{document}

Font package mathabx

If package mathabx is used (also changes other math symbols), then the symbol is called \Dashv:

\documentclass{article}
\usepackage{mathabx}
\begin{document}
\[ A \Dashv B \]
\end{document}

Answer 2

Simply use \Dashv from mathabx package.

You can find almost any symbol in The comprehensive LaTeX Symbol List.

Answer 3

This would be the logicians' way, I think. Note that the project authors made a deliberate decision not to adjust the length of the vertical lines according to context. Horizontal lengths are adjusted depending on what is above and below them, for example.

\documentclass{article}
\usepackage{turnstile}

\begin{document}

\[
  A \sdtstile{}{} B
\]
\[
  A \ndststile{}{} B
\]

\end{document}

The advantage of using turnstile, as far as I can see, is that it is extremely flexible and can produce pretty much any turnstile you might want. It also works hard to get the spacing right when something is required above or below the horizontal. (Commands such as \vDash don't adjust the spacing and line lengths correctly.)