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

Question

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 '19 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 '19 at 12:10
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 '19 at 15:17
@Davislor \mbox{\reflectbox{C}} seems to produce an ugly symbol, haha! — M. Logic, Mar 02 '19 at 01:32
@Kuttens: By the way, what you've presented is not a minimal example... — Werner, Mar 02 '19 at 02:32
@Kuttens Maybe \mathrel{\mbox{\reflectbox{\sffamily C}}} would look a little better? I also have a little solution in TIKZ, but I felt it was redundant with Sandy G’s great answer. — Davislor, Mar 02 '19 at 04:05
Do you have a scan of Peano's original use of this symbol in 1889? — AndréC, Mar 02 '19 at 06:32
@AndréC yes, very similar to but not the same as the universal quantifier \forall. — M. Logic, Mar 02 '19 at 14:25

score 7 · Answer 1 · answered Feb 28 '19 at 15:08

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}

@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 03 '19 at 20:19

score 1 · Answer 2 · answered Feb 28 '19 at 14:11

1

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?.

answered Feb 28 '19 at 14:11

1

OP requested the same size and weight as \medcirc. This doesn't really do it. – Sandy G Feb 28 '19 at 15:20

M. Logic · Accepted Answer · 2019-03-04T01:16:37.980

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).

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

3 Answers3