# How do I create a major arc open to the left?

First a minimal working sample is as following:

\documentclass{amsart}
\usepackage{txfonts}

\begin{document}

\end{document}


Goal: I want a math symbol which is like a circle but misses a left part as in the following picture. Any help is welcome. I hope it has the same line weight and size as \medcirc in the txfonts package.

• What is this mathematical symbol? What does it mean? Why doesn't it exist in standard packages? – AndréC Feb 28 at 10:42
• Just for fun, here is a picture version : \begin{picture}(0,0)(0,-2)\put(0,0){\circle{2}}\textcolor{white}{\linethickness{.3mm}\put(-1.5,0){\line(1,0){1}}}\end{picture} that requires xcolor package. – Kpym Feb 28 at 12:10
• Maybe \mbox{\reflectbox{C}}? – Davislor Feb 28 at 13:34
• Not really a duplicate. Detexify doesn't recognize it. And I'm not finding it in the comprehensive list. I think you may have to design your own. – Sandy G Feb 28 at 15:17
• @AndréC It's used personally by Peano in 1889. – Mogic Mar 2 at 1:30

Here is a solution that uses \ooalign to overlay a white rectangle on part of a \medcirc.

\mathchoice is used to allow your symbol to appear in script or scriptscript styles. You can edit the \rule arguments to adjust height and thickness of the opening in each style.

\documentclass{amsart}
\usepackage{txfonts,color}

\newcommand{\arcl}{\mathchoice%
{\mathbin{\ooalign{\hfil$\medcirc$\hfil\cr\textcolor{white}{\rule[.25ex]{.2em}{.65ex}}\hfil\cr}}}
{\mathbin{\ooalign{\hfil$\medcirc$\hfil\cr\textcolor{white}{\rule[.25ex]{.2em}{.65ex}}\hfil\cr}}}
{\mathbin{\ooalign{\hfil$\scriptstyle\medcirc$\hfil\cr\textcolor{white}{\rule[.2ex]{.2em}{.4ex}}\hfil\cr}}}
{\mathbin{\ooalign{\hfil$\scriptscriptstyle\medcirc$\hfil\cr\textcolor{white}{\rule[.15ex]{.2em}{.25ex}}\hfil\cr}}}
}

\begin{document}

$a\medcirc b_{a\medcirc b_{a\medcirc b}}$

$a\arcl b_{a\arcl b_{a\arcl b}}$

\end{document}

• I got a more suitable way for which see the posted answer. – Mogic Mar 2 at 2:20
• @Kuttens, just watch the spacing on that other solution. You should enclose it in \mathbin{} to get the same spacing as \medcirc. – Sandy G Mar 3 at 20:19

Is this what you need?

\documentclass{article}
\usepackage{amsmath}
\usepackage{tipa}
\newcommand{\yoursymbol}{\text{\textopeno}}
\begin{document}
$a^2+\yoursymbol^2+\frac{2}{\yoursymbol}=0$
\end{document}


I get this from Detexify. Therefore, your question is possibly a duplicate of How to look up a symbol or identify a math symbol or character?.

• OP requested the same size and weight as \medcirc. This doesn't really do it. – Sandy G Feb 28 at 15:20

With an improvement of @Kpym 's answer and the help of pict2e and scalerel packages, I got a suitable way:

\documentclass{amsart}
\usepackage{pict2e}
\usepackage{scalerel}
\newcommand{\peanoall}{\mathbin{%
\scalerel*{%
\begin{picture}(5,5.5)%
\put(2.5,2.75){\circle{5.5}}
\textcolor{white}{\linethickness{1.25mm}\put(2.5,2.75){\line(-1,0){3}}}
\end{picture}
}{\forall}%
}}
\begin{document}

$\phi\peanoall x,y\cdots\psi$

\end{document}


It could change the size with its location (normal texts or footnotes or scripts).