Wie kann ich mit der neuen graphs-Library von TikZ die chains-Library ersetzen?

Als Kommentar zum Feature Request „Allow Labels on all chain edges“ schreibt Till Tantau Folgendes:

The chains library is now outdated. The graphs library and its friends are more powerful and easier to use.

Die chains–Library ist jetzt überholt. Die graphs–Library und ihre Freunde sind leistungsfähiger und einfacher zu benutzen.

Meine Frage ist deshalb, wie ich das folgende, einfache chains–Beispiel aus dem Manuel mit der graphs–Library (und Freunden?) rekreieren kann.

Code

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\documentclass[tikz]{standalone}
\usepackage{tikz}
\usetikzlibrary{chains,scopes}
\begin{document}
\begin{tikzpicture}[
  every on chain/.style=join,
  every join/.style=->,
  node distance=+2mm and +1cm]
{ [start chain=trunk]
  \node [on chain] {A};
  \node [on chain] {B};
  { [start branch=numbers going below] }
  { [start branch=greek going above] }
  \node [on chain] {C};
  { [continue branch=numbers]
    \node [on chain] {1};
    \node [on chain] {2};
  }
  { [continue branch=greek]
    \node [on chain] {$\alpha$};
    \node [on chain] {$\beta$};
  }
}
\end{tikzpicture}
\end{document}
 
 
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