3

An ST-trace is a string with additional back-reference arc or arrows which may cross. An example may be seen at page 13 of http://kilby.stanford.edu/~rvg/pub/STbisimulation.pdf

So, basically, this is a string like $a^+b^+c^+a^-b^-$, but with an arc or arrow, under or over, from the $a^-$ back to the $a^+$ and from the $b^-$ back to the $b^+$.

How on earth can I typeset this in LaTeX?

6

Here's a possibility with tikz-cd:

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

\begin{document}
\[
\begin{tikzcd}[column sep=.7em]
b^+ \arrow[rrr,dash,bend left] &
a^+ &
a^+ \arrow[rrr,dash,bend left] &
b^- &
a^+ \arrow[rrr,dash,bend left] &
a^- &
b^+ &
a^-
\end{tikzcd}
\]
\end{document}

enter image description here

You can mark the “crossing over” with

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

\begin{document}
\[
\begin{tikzcd}[column sep=1.4em]
b^+ \arrow[rrr,dash,bend left=40] &
a^+ &
a^+ \arrow[rrr,dash,bend left=40,crossing over] &
b^- &
a^+ \arrow[rrr,dash,bend left=40,crossing over] &
a^- &
b^+ &
a^-
\end{tikzcd}
\]
\end{document}

enter image description here

1
  • I accepted this answer (and not the other), because I find the code nicer and cleaner. Semantically, the arcs are back-references, so I'd use \arrow[lll,...] in appropriate places instead of your \arrow[rrr,...]. – Uli Fahrenberg May 5 '15 at 14:58
3

A solution with pstricks, and more sprifically with the psmatrix environment of pdt-node. With the pdf option, it can be compiled with pdflatex provided you set the --enable-shellescape switch, or __enable-write18 for MiKTeX:

\documentclass[12pt, pdf]{standalone}%

\usepackage{pst-node}

\begin{document} 

 $ \psset{arcangle = 45}
\begin{psmatrix}[nodesep =3pt,colsep = 2em, arcangle = 30]
[name = a0] a^+ & [name = b0] b^+ & c^+ & [name = a1] a^- & [name = b1]b^-
\ncarc{a0}{a1}
\ncarc[border = 1pt, bordercolor = white]{b0}{b1}
\end{psmatrix} $ 

\end{document} 

enter image description here

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