# Circular arrow in tikz-cd

How do I draw a circular arrow (to indicate commutativity) in tikz-cd, similar to the one in the middle of the following diagram?

(Image from this question.)

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Use of PDFlatex or XeLaTeX with $\circlearrowleft$ from amssymbol/amsmath with scalable size.

Code

\documentclass[border=2pt]{standalone}
\usepackage{amssymb,amsmath}
\usepackage{tikz-cd}
\usetikzlibrary{arrows}

\usepackage{tikz}

\begin{document}
%\tikzset{commutative diagrams/.cd, arrow style=tikz,diagrams={>= latex}}

\begin{tikzcd}[row sep=2cm,column sep=2cm,inner sep=1ex]
\bar A  \arrow[thick,swap] {d}{\bar F_q}
&
\bar A_E   \arrow[thick,swap]{l}[name=U]{\pi^\star}
\arrow[thick]{d}{\bar F_{q,E}}
\\
\bar A     & \bar A_E     \arrow[thick]{l}[name=D]{\pi^\star}
\arrow[to path={(U) node[midway,scale=3] {$\circlearrowleft$}  (D)}]{}
\end{tikzcd}

\end{document}

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You can draw an arc using the option -> following the syntax described in the documentation in the Arc Path Reconstruction.

\draw (starting point x, starting point y) arc (starting angle:ending angle:radius);

For instance this code will produce an arrow like the one requested

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\draw[step=1cm,gray!50,very thin] (-1.9,-1.9) grid (5.9,5.9);
\draw[very thick,->] (0,0) -- (4.5,0) node[anchor=north west] {\bf{x axis}};
\draw[very thick,->] (0,0) -- (0,4.5) node[anchor=south east] {\bf{y axis}};
\foreach \x in {0,1,2,3,4}
\draw (\x cm,1pt) -- (\x cm,-1pt) node[anchor=north] {$\mathbf{\x}$};
\foreach \y in {0,1,2,3,4}
\draw (1pt,\y cm) -- (-1pt,\y cm) node[anchor=east] {$\mathbf{\y}$};
\draw[thick, ->] (3,2) arc (0:270:1cm);% syntax (starting point coordinates) arc (starting angle:ending angle:radius)
\end{tikzpicture}
\end{document}


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At least an explanation of how to include this into tikz-cd would be great. –  Manuel Jul 9 at 8:42

If you are willing to use Lua- or XeLaTeX:

% arara: lualatex

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{unicode-math}

\begin{document}
\begin{tikzcd}[row sep=5pt, column sep=5pt]
\overbar{A} \arrow[swap, "\overbar{F}_q"]{dd} &  &  \overbar{A}_E
\arrow["\overbar{F}_{q,E}"]{dd} \arrow[swap, "\pi^\ast"]{ll}  \\
& \cwopencirclearrow & \\
\overbar{A} & &  \overbar{A}_E \arrow["\pi^\ast"]{ll}
\end{tikzcd}
\end{document}
`

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