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I've tried detexify, but it does not identity the symbol I saw in a textbook "A Mathematical Introduction to Logic", by Herbert Enderton.

The symbol is composed of two parts. The left looks like the \models and the right looks like its mirror image. It stands for tautological equivalence in the book.

I am looking for either the right hand symbol so I can create the symbol, or the combination symbol.

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1 Answer

up vote 13 down vote accepted

See The Comprehensive Symbol List. Examples:

MnSymbol

\documentclass{article}
\usepackage{MnSymbol}
\begin{document}
$\rightmodels\leftmodels$
\end{document}

Result MnSymbol

mathabx

\documentclass{article}
\usepackage{mathabx}
\begin{document}
$\vDash\Dashv$
\end{document}

Result mathabx

Symbol composition a la LaTeX

See Enrico Gregorio's comment. The definition of \models in LaTeX joins a vertical line | with the double horizontal line \RelBar.

\documentclass{article}

\DeclareRobustCommand*{\tautequiv}{%
  \mathrel{|}\joinrel\Relbar
  \Relbar\joinrel\mathrel{|}%
}

\begin{document}
\[ \tautequiv^{\tautequiv^{\tautequiv}} \]
\end{document}

Result compsition

\reflectbox

If the current math fonts do not provide the mirrored \models, then package graphics can help:

\documentclass{article}
\usepackage{graphicx}

\newcommand*{\tautequiv}{%
  \models\mirrormodels
}
\makeatletter
\newcommand*{\mirrormodels}{%
  \mathrel{%
    \mathpalette\reflectmathsymbol\models
  }%
}
\newcommand*{\reflectmathsymbol}[2]{%
  \reflectbox{$\m@th#1#2$}%
}
\makeatother

\begin{document}
\[ \tautequiv^{\tautequiv^{\tautequiv}} \]
\end{document}

Result \reflectbox

Package accsupp

The /ActualText feature of the PDF format improves the copy&paste behaviour for PDF viewers the support this feature (e.g. Adobe Reader). Example:

\documentclass{article}

\usepackage{accsupp}

\DeclareRobustCommand*{\tautequiv}{%
  \BeginAccSupp{unicode,method=hex,ActualText=22A8 2AE4}%
    \mathrel{|}\joinrel\Relbar
    \Relbar\joinrel\mathrel{|}%
  \EndAccSupp{}%
}

\begin{document}
\[ \tautequiv^{\tautequiv^{\tautequiv}} \]
\end{document}
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2  
Why not \DeclareRobustCommand\tautequiv{\Relbar\joinrel\mathrel{|}}, that is doing the same as \models but backwards? –  egreg Jan 23 '13 at 10:28
    
@egreg "All roads lead to Rome." :-) Answer extended, also package accsupp added. –  Heiko Oberdiek Jan 23 '13 at 11:26
3  
please observe that both the MnSymbol and mathabx packages change a lot of other symbols as well, so if just one or two symbols are wanted, one answer to this question shows how to get that result. –  barbara beeton Jan 23 '13 at 13:54
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