Weird problem in Wick contraction

Question

I am facing a problem in Wick contraction that totally weird. There are two pieces : $\langle \wick{\c1 p', \c2 k' \vert \overline{\c2 \psi} \c3 \psi \overline{\c1 \psi} \c4 \psi \vert \c4p, \c3 k} \rangle$and $\langle \wick{\c1 p', \c3 k' \vert \overline{\c2 \psi} \c3 \psi \overline{\c1 \psi} \c4 \psi \vert \c4 p, \c2 k} \rangle$. The first one gives a perfect expression but the second one is giving weird result. Somehow one contraction is missing

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What am I doing wrong here?

Answer 1

How about this?

\documentclass{article}
\usepackage{simpler-wick}
\begin{document}
$\langle
\wick{
  \c1{p'},
  \c2{k'} \vert
  \c2{\overline{\psi}}
  \c3{\psi}
  \c1{\overline{\psi}}
  \c4{\psi}
  \vert
  \c4{p},
  \c3{k}
}
\rangle$
and
$\langle
\wick{
  \c1{p'},
  \c3{k'}
  \vert
  \c2{\overline{\psi}}
  \c3{\psi}
  \c1{\overline{\psi}}
  \c4{\psi}
  \vert
  \c4{p},
  \c2{k}
}
\rangle$
\end{document}