I'm trying to display some axioms and operational rules with LaTeX.
Those are basically . They work quite well when used with frac, but it's not really nice, I'd like the fraction line to be a bit longer.
I know that sounds a bit vague, so here is a picture of what I am trying to achieve. I'm pretty sure that document has been typeset in LaTeX, so it should be doable.
\newcommand\bigfrac[2]{%
\begin{array}{c}
#1 \\
\hline
#2
\end{array}}
\newcommand\bigfrac[2]{\begin{array}{c}#1\\\hline\vspace{1pt}#2\end{array}} but that just increased the space between the two lines in the picture.
Commented
Jun 25, 2011 at 12:55
\begingroup\setlength\extrarowheight{1pt} before \begin{array} and \endgroup after \end{array}. Load the array package.
Here's an extended version of \frac, supporting an optional argument for a wider line:
\documentclass{article}
\DeclareRobustCommand{\frac}[3][0pt]{%
{\begingroup\hspace{#1}#2\hspace{#1}\endgroup\over\hspace{#1}#3\hspace{#1}}}
\begin{document}
\[
\frac{x}{y} \quad \frac[5pt]{x}{y}
\]
\end{document}
Of course you can define your own frac command similar instead of redefining the existing \frac, also with a default value bigger than 0pt.
The definition is similar to the definition in amsmath.sty, except that file is using \@@over.
Or, you could define your own macro using the original \frac:
\DeclareRobustCommand{\widefrac}[3][5pt]{%
\frac{\hspace{#1}#2\hspace{#1}}{\hspace{#1}#3\hspace{#1}}}
...
\widefrac{x}{y} ... \widefrac[8pt]{x+y}{y}
\over together with amsmath will lead to Package amsmath Warning: Foreign command \over.
Commented
Jun 25, 2011 at 13:23
amsmath the command \@@over can be used instead, exactly in the same way plus \makeatletter and \makeatother. amsmathdefines: \@saveprimitive\over\@@over.
\frac and use it here? Or use \genfrac provided by amsmath.
\frac. Of course it could be done similar with \genfrac.
In case you really want fractions with a longer line, you can just pad both numerator and denominator with spaces. (Padding the longer of the two would acually suffice.) \frac{\ a\ }{\ b\ } gives
For a longer line use, e.g., \quad instead of \ .
You should consider to use a dedicated package to write your axioms; the bussproofs package could be an option:
\documentclass{article}
\usepackage{bussproofs}
\usepackage{amsmath}
\newcommand*\LArrow[1][a]{\xrightarrow{\phantom{a}#1\phantom{a}}}
\begin{document}
\begin{prooftree}
\AxiomC{$x\LArrow x^\prime$}
\UnaryInfC{$x+y\LArrow x^\prime$}
\end{prooftree}
\end{document}
To work with displayed math environments, a better option would be to use the proof package. A little example:
\documentclass{article}
\usepackage{proof}
\usepackage{amsmath}
\newcommand*\PA{\phantom{a}}
\newcommand*\LArrow[1][a]{\xrightarrow{\PA#1\PA}}
\begin{document}
\begin{equation}
\infer{\PA x+y\LArrow x^\prime\PA}{x\LArrow x^\prime}
\qquad
\infer{\PA x+y\LArrow y^\prime\PA}{y\LArrow y^\prime}
\qquad
\infer{\PA x+y\, \downarrow\PA}{x\,\downarrow}
\qquad
\infer{\PA x+y\, \downarrow\PA}{y\,\downarrow}
\end{equation}
\end{document}
Another solution is to use the \phantom{} command, which renders the exact whitespace the exact same size as its argument.
For example,
\documentclass{article}
\usepackage{proof}
\usepackage{amsmath}
\begin{align*}
\varphi &= 1+ \frac{1}{1 + \cfrac{1}{\varphi}}\\[.5cm]
%
%
\varphi &= 1+ \frac{ \phantom{\longrightarrow} 1 \phantom{\longrightarrow} }{1
+ \cfrac{1}{\varphi}}
\end{align*}
\end{document}
which returns
