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I want a symbol for an equivalence relation meaning “on the same hyperbola $xy=c$”.

Is there a standard notation? If not, I'm thinking of something on the tune of

hyperbolic equivalence

Any idea of a similar sign, or how to build one, by stacking or otherwise, in a way compatible with arXiv, LNCS and AMS environments?

1 Answer 1

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Your symbol is a bit complicated. Since I know of no standard symbol, I suggest this:

enter image description here

which is formed by overlaying two standard symbols (\asymp and -) and requires no additional packages. It looks (to me) like a hyperbolic version of \equiv ().

\documentclass{article}

\newcommand{\samehyp}{\mathrel{\ooalign{\hfil$\asymp$\hfil\cr\hfil$-$\hfil\cr}}}

\begin{document}

$(a,b)\samehyp(c,d)$

\end{document}

For general instructions on how to build your own symbols, I suggest this question and its answers.

Note: If you plan to use this symbol in \scriptstyle or \scriptscriptstyle you will need a more complicated version that will adapt to style changes:

enter image description here

\documentclass{article}

%\newcommand{\samehyp}{\mathrel{\ooalign{\hfil$\asymp$\hfil\cr\hfil$-$\hfil\cr}}}
\makeatletter
\newcommand{\samehyp}{\mathrel{\mathpalette\s@mehyp\relax}}
\newcommand{\s@mehyp}[2]{%
  \ooalign{%
    $\m@th#1\asymp$\cr
    \hidewidth$\m@th#1-$\hidewidth\cr
  }%
}
\makeatother


\begin{document}

$(a,b)\samehyp(c,d)_{(a,b)\samehyp(c,d)_{(a,b)\samehyp(c,d)}}$

\end{document}

If you really want the symbol you sketched, you'll probably have to design it yourself. I suggest tikz (for designing the symbol) and scalerel to make it the same size as a symbol of your choice (I picked +).

enter image description here

\documentclass{article}

\usepackage{tikz,scalerel}

\newcommand{\samehyp}{\mathrel{\scalerel*{\tikz{\draw[line width=2pt](0,.3)--(1,.3)(0,.5)--(1,.5)(0,.7)--(1,.7)(.6,1)to[out=-90,in=180](1,.6)(.4,0)to[out=90,in=0](0,.4);}}{+}}}

\begin{document}

$(a,b)\samehyp(c,d)$

\end{document}
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  • Many thanks. The combination of \asymp and - has the advantage of simplicity and readability. The code given works nicely when standalone, but for some reason fails in my ams context. A workaround for me was to use the \makeatletter…\makeatother found there then \newcommand{\samehyp}{\charfusion[\mathbin]{\asymp}{-}}
    – fgrieu
    Commented May 10, 2022 at 21:19

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