%%
%% The LaTeX Companion, 3ed
%%
%% Example 8-5-11 on page I-638 in "Basic objects".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{159.0pt}

%StartShownPreambleCommands
\usepackage{tikz}
%StopShownPreambleCommands

\begin{document}
\begin{tikzpicture}
\tikzset{my loop/.style=
  {to path={.. controls +(80:1) and +(100:1)
            .. (\tikztotarget) \tikztonodes}}}

\draw[dotted,thick](0,2) to (2,2);
\draw[blue,thick](0,1) to[out=60,in=60] (2,1);
\node[circle,draw](a) at (1,0) {T};
\draw [->](a) to[my loop] (a);
\end{tikzpicture}
\end{document}