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How to get the $\models$-symbol vice-versa to form a symbol for semantically equivalent like the following: =||=

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I'm not sure what's being asked here. Can you provide a little more? –  qubyte May 17 '12 at 11:41
    
this symbol is now in unicode as Ux27DA and will ultimately be included in unicode-compliant math fonts with (presumably) the command name \DashVDash. –  barbara beeton May 17 '12 at 12:42

2 Answers 2

up vote 6 down vote accepted

\models in the standard fonts is a made up symbol

\DeclareRobustCommand
  \models{\mathrel{|}\joinrel\Relbar}

So you could do a matching combination:

\documentclass{article}


%\DeclareRobustCommand
%  \models{\mathrel{|}\joinrel\Relbar}
\DeclareRobustCommand
  \sledommodels{\Relbar\joinrel\mathrel{\|}\joinrel\Relbar}

\begin{document}

\[A \models B\]
\[A \sledommodels B\]

\end{document}

result

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Any particular reason for preferring \mathrel{\|} over \parallel, which is already mathrel? –  dubiousjim Aug 19 at 1:10
    
@dubiousjim not really (at least not from me;-) I just copied the definition of \models and reflected it. –  David Carlisle Aug 19 at 8:16

If you are in a LaTeX-only environment (for example, MathJax), consider this:

\newcommand{\rmodels}{\ensuremath{\mathrel{=\!\!\!|}}}

Semantic equivalence can, for example, look like this:

\newcommand{\semeq}{\ensuremath\mathrel{\rmodels\!\models}}}

The result (pdflatex):

enter image description here

Depending on your context of conventions, \models\rmodels might be what you want:

enter image description here

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