How to adjust a proof tree using bussproofs?

Question

I used bussproofs.sty to create this natural deduction rule:

Source:

\documentclass{beamer}

\usepackage{bussproofs}

\begin{document}

\begin{frame}

    \AxiomC{$A\vee B$}
    \AxiomC{[$A$]}
      %\vspace{-2em}
      \noLine
      \UnaryInfC{\vdots}
      \noLine
      \UnaryInfC{$C$} 
    \AxiomC{[$B$]}
      \noLine
      \UnaryInfC{$\vdots$}
      \noLine
      \UnaryInfC{$C$}
    \RightLabel{$\vee$E}
    \TrinaryInfC{$C$}
    \DisplayProof 

\end{frame}

\end{document}

How can I get less space between the assumptions and the vertical dots? I tried \vspace with a negative distance but it worked on another block.

Answer 1

You can smash the \vdots and give them the same height as a capital letter.

\documentclass{beamer}

\usepackage{bussproofs}

\newcommand{\svdots}{\vphantom{\ensuremath{X}}\smash{\vdots}}

\begin{document}

\begin{frame}

    \AxiomC{$A\vee B$}
    \AxiomC{[$A$]}
      \noLine
      \UnaryInfC{\svdots}
      \noLine
      \UnaryInfC{$C$}
    \AxiomC{[$B$]}
      \noLine
      \UnaryInfC{\svdots}
      \noLine
      \UnaryInfC{$C$}
    \RightLabel{$\vee$E}
    \TrinaryInfC{$C$}
    \DisplayProof

\end{frame}

\end{document}

Answer 2

Going down to plain TeX helped:

\documentclass{beamer}

\usepackage{bussproofs}

\begin{document}

\begin{frame}

    \AxiomC{$A\vee B$}
    \AxiomC{[$A$]}
      %\vspace{-2em}
      \def\extraVskip{-2pt}
      \noLine
      \UnaryInfC{\vdots}
      \def\extraVskip{2pt}
      \noLine
      \UnaryInfC{$C$} 
    \AxiomC{[$B$]}
      \def\extraVskip{-2pt}
      \noLine
      \UnaryInfC{$\vdots$}
      \def\extraVskip{2pt}
      \noLine
      \UnaryInfC{$C$}
    \RightLabel{$\vee$E}
    \TrinaryInfC{$C$}
    \DisplayProof 

\end{frame}

\end{document}