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I am using the semantic package to write inference rules. I need to put a there exists symbol which is standard to LaTeX using $\exists$. However, when used within the semantic package's inference command as follows:

\inference[case$_0$]{$\exists$ I}{test}

several errors are encountered :

(./semantics.aux) (/usr/share/texmf-texlive/tex/latex/ucs/ucsencs.def)
! Missing $ inserted.
<inserted text>
$
l.42 \inference[case$_0$]{$\exists$ I}
{test}
! Extra }, or forgotten $.
\@processPremiseLine ...ce \end \hskip \@@pSpace }
\fi \fi \def \sem@tmp {#2}...
l.42 \inference[case$_0$]{$\exists$ I}
{test}
! Missing $ inserted.
<inserted text>
$
l.42 \inference[case$_0$]{$\exists$ I}
{test}
! Missing } inserted.
<inserted text>
}
l.42 \inference[case$_0$]{$\exists$ I}
{test}
[1] (./semantics.aux) )

Can anyone suggest what I can do please?

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2 Answers 2

up vote 2 down vote accepted

You can "box" the item using \ensuremath:

enter image description here

\documentclass{article}
\usepackage{semantic}% http://ctan.org/pkg/semantic
\begin{document}
\inference[case$_0$]{\ensuremath{\exists~I}}{test}
\end{document}

Note the forced spacing as a result of the tie ~. This may just be your preference, which I've stuck to.

share|improve this answer
    
thank you .. thats what I needed! –  aseychell Dec 7 '11 at 8:03

The mandatory arguments seem to be in mathmode by definition, so you do not need to enter mathmode. Remove the dollar signs and it works fine.

\documentclass{article}
\usepackage{semantic}
\begin{document}
\inference[case$_0$]{\exists I}{test}
\end{document}
share|improve this answer
    
Damn, I'm too slow ... –  Torbjørn T. Dec 7 '11 at 8:05
    
works nice aswell .. thanks! –  aseychell Dec 7 '11 at 8:18

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