Unusual bussproofs derivation

Question

I'm trying to typeset proofs like these in bussproofs (to keep them consistent with the rest of my proofs) but I can't figure out a good way to do so:

I've tried using various combinations of \rootAtTop to almost no success (e.g. I'm unable to add the second pair of vdots in the first derivation without messing everything up; letters I'm the second derivation fall off their lines and don't align).

(1)

    \AxiomC{$A$} \noLine    
\UnaryInfC{$\strut \vdots$} 
    \rootAtTop
    \AxiomC{$\strut \vdots$}  \noLine
    \UnaryInfC{$x \vphantom{y}$} 
    \AxiomC{$\strut \vdots$}  \noLine
    \UnaryInfC{$y$} 
\BinaryInfC{$xy$}
\rootAtBottom   
    \AxiomC{$B$} \noLine
\UnaryInfC{$\strut \vdots$} 
\TrinaryInfC{$C$}
\DisplayProof

(2)

\rootAtTop
        \AxiomC{$x \vphantom{y}$} \noLine
    \UnaryInfC{$\ \vphantom{/}$}
        \AxiomC{$y \vphantom{/}$}
        \AxiomC{$\ \vphantom{/}$}
        \AxiomC{$\ \vphantom{/}$}
    \TrinaryInfC{$yz$} 
\BinaryInfC{$xyz$}
\rootAtBottom
    \AxiomC{}
\BinaryInfC{$ xy$}
\AxiomC{$z$}
\BinaryInfC{$C$}
\DisplayProof

Has anyone else encountered proofs like these or have any suggestions?

Answer 1

Neither bussproofs nor its more flexible successor ebproof is well-suited to drawing proofs of the kind you need here. Consistency of typesetting is surely a worthy goal, but there are times when a tool just doesn't do what you need.

The proofs would not be hard to do with a tabular or array. Here, I've used a TikZ matrix. Possibly a standard tabular or array would be easier, but the matrix library was in my mind.

Here, first, are the results.

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}
\begin{tikzpicture}
  \matrix (e) [matrix of math nodes, nodes in empty cells, nodes={text depth=2.5pt, text height=7.5pt}]
  {
    A && xy && B\\
    \vdots &&&& \vdots\\
    \vdots & x && y & \vdots\\
    \vdots & \vdots && \vdots & \vdots\\
    && C && \\
  };
  \draw (e-2-2.center -| e-3-2.west) -- (e-2-4.center -| e-4-4.east) (e-4-1.south -| e-1-1.west) -- (e-4-5.south -| e-1-5.east);
\end{tikzpicture}
\begin{tikzpicture}
  \matrix (p) [matrix of math nodes, nodes in empty cells, nodes={text depth=2.5pt, text height=7.5pt}]
  {
    & xyz & & & \\
    & & yz & & \\
    x & y & & \\
    xy & & & z \\
    & & C & & \\
  };
  \draw (p-1-1.south west) -- (p-1-3.south -| p-2-3.east) (p-2-2.south west) -- (p-2-3.south east) (p-3-1.south -| p-4-1.west) -- (p-3-2.south east) (p-4-1.south west) -- (p-4-4.south east) ;
\end{tikzpicture}
\end{document}