Vertical alignment in bussproofs

Question

Consider the following code:

\documentclass{article}
\usepackage{graphicx}

\usepackage{bussproofs}
\newenvironment{bprooftree}
  {\leavevmode\hbox\bgroup}
  {\DisplayProof\egroup}

\begin{document}

\[
  \begin{bprooftree}
  \AxiomC{$ $}
  \LeftLabel{R1:}
  \UnaryInfC{s}
  \end{bprooftree}
\qquad
  \begin{bprooftree}
  \AxiomC{$s_1,\cdots,s_n$}
  \LeftLabel{R2:}
  \UnaryInfC{s}
  \end{bprooftree}
\]

\end{document}

The result is the following:

As you can see from the picture R1 and R2 are not vertically aligned (at least not in the way a would like). How can I achieve a correct alignment?

Note: I do not remember exactly why I added the line with \newenvironment but I think that it was due to the conflict with another package that I use: qtree.

Answer 1

Each tree is vertically centered on the math axis with respect to its contents. If you want two of them to have the same size, you need to use phantoms.

I also added a different style, with better control of the space between the trees.

\documentclass{article}
\usepackage{graphicx}

\usepackage{bussproofs}
\newenvironment{bprooftree}
  {\leavevmode\hbox\bgroup}
  {\DisplayProof\egroup}

\begin{document}

\[
  \begin{bprooftree}
  \AxiomC{$\vphantom{s_1,\cdots}$}
  \LeftLabel{R1:}
  \UnaryInfC{s}
  \end{bprooftree}
\qquad
  \begin{bprooftree}
  \AxiomC{$s_1,\cdots,s_n$}
  \LeftLabel{R2:}
  \UnaryInfC{s}
  \end{bprooftree}
\]

\[
  \AxiomC{$\vphantom{s_1,\cdots}$}
  \LeftLabel{R1:}
  \UnaryInfC{s}
  \DisplayProof
\qquad
  \AxiomC{$s_1,\cdots,s_n$}
  \LeftLabel{R2:}
  \UnaryInfC{s}
  \DisplayProof
\]

\end{document}