Fraction with double line with ams environment

Question

I am not sure if this counts as a duplicate question, but I would like to have a fraction where the delimiter consists of two lines. I tried using the Tfrac solution at Fraction with doubled line and it works fine, until I use an ams environment in the denominator and get the following output

I assume it is related to the usage of ooalign. I tried to look up online how I should go about this, but I can't seem to find much.

My code is

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\newcommand{\Tfrac}[2]{%
  \ooalign{%
    $\genfrac{}{}{1.2pt}1{#1}{#2}$\cr%
    $\color{white}\genfrac{}{}{.4pt}1{\phantom{#1}}{\phantom{#2}}$}%
}
$
\Tfrac
    {
        \phantom{test}
    }
    {
        \mathtt{B} \oplus {\mathit{repeat}:, \mathtt{B?[int]; S'}}
        , \leq ,
        \mathtt{B \oplus}
        \left{
        \begin{aligned}
            & \mathit{notify} : \mathtt{B![bool]; end} \
            & \mathit{repeat}: S_4 \
            & \mathit{stop}: \mathtt{end} \
        \end{aligned}
        \right}
    }
$

Edit: To show the intended use, I would like to end up with something like this, but with double lined fractions instead.

From your example it looks more like you want a double accent bar. — mickep, Dec 29 '23 at 14:45
In this example no, however there will be cases where I will also have these type of fractions as the numerator. The end result would be a derivation tree, so I would ideally need to be able to nest these fractions, which I currently can, as long as I don't use the ams environment — Filu, Dec 29 '23 at 14:46
@egreg could you please guide me in the right direction? I will also add an example of how I would like to use it later on, to maybe give a better explanation of what I mean by nested — Filu, Dec 29 '23 at 14:52
@egreg thank you for suggesting this, I found the ebproof package and it seems much more suited for what I want to achieve — Filu, Dec 29 '23 at 15:13

score 2 · Accepted Answer · answered Dec 29 '23 at 14:54

I think that you're using the wrong tool. Anyway, a simple modification of my code in another answer to the question you link to will do.

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newlength{\doublefracgap}
\setlength{\doublefracgap}{0.75pt}
\DeclareRobustCommand{\doublefrac}[2]{%
  \mathinner{\mathpalette\doublefrac@{{#1}{#2}}}%
}
\newcommand{\doublefrac@}[2]{\doublefrac@@#1#2}
\newcommand{\doublefrac@@}[3]{%
  \ooalign{%
    \raisebox{\doublefracgap}{\normalbaselines$\m@th#1\frac{#2}{\phantom{#3}}$}\cr
    \raisebox{-\doublefracgap}{\normalbaselines$\m@th#1\frac{\phantom{#2}}{#3}$}\cr
  }%
}
\newcommand{\ddoublefrac}[2]{{\displaystyle\doublefrac{#1}{#2}}}
\newcommand{\tdoublefrac}[2]{{\textstyle\doublefrac{#1}{#2}}}
\makeatother
\begin{document}
[
\doublefrac
    {
        \phantom{test}
    }
    {
        \mathtt{B} \oplus {\mathit{repeat}:, \mathtt{B?[int]; S'}}
        , \leq ,
        \mathtt{B} \oplus
        \left{
        \begin{aligned}
            & \mathit{notify} : \mathtt{B![bool]; end} \
            & \mathit{repeat}: S_4 \
            & \mathit{stop}: \mathtt{end} \
        \end{aligned}
        \right}
    }
]
\end{document}

The difference is in the \normalbaselines declarations.

I fixed \mathtt{B\oplus} to \mathtt{B}\oplus, as the former is wrong as it produces wrong spacing (and \mathtt around \oplus does nothing at all).

Fraction with double line with ams environment

1 Answers1