Left-aligned logicproof

Question

I'm typesetting a natural deduction proof. These consist of several numbered statements along with justifications. I'm using the logicproof package, and a minimal example looks something like this:

\documentclass[article]
\usepackage{logicproof}
\begin{document}
text
\begin{logicproof}{0}
    statement & justification
\end{logicproof}

It compiles into this (black bars show geometry of page):

I'd like the proof to be aligned on the left (as with the rest of the text), but I can't see any mention of how to do this in the package documentation. I believe that the package uses tabular under the hood.

I've tried to redefine \center to hack around this, and the following code seems to do the trick - but I'm unsure if this is good practice or not.

\def\center{\trivlist\item\relax}
\def\endcenter{\endtrivlist}

Is there a better approach? Should I use \renewcommand instead?

Answer 1

In the definition of the logicproof environment the commands \center and \endcenter are used.

The easiest way to fix this is by using the \patchcmd command from the etoolbox package:

\documentclass{article}
\usepackage{logicproof,etoolbox}

\patchcmd{\logicproof}{\center}{\flushleft}{}{}
\patchcmd{\endlogicproof}{\endcenter}{\endflushleft}{}{}

\begin{document}
\noindent text
\begin{logicproof}{0}
    statement & justification
\end{logicproof}

\end{document}

Another fix is to simply replace these with \flushleft and \endflushleft in a \renewenvironment{logicproof} in your preamble:

\documentclass{article}
\usepackage{logicproof}

\makeatletter
\renewenvironment{logicproof}[1]{%
  \setcounter{lp@line}{0}%
  \setcounter{lp@nested}{0}%
  \setcounter{lp@total@nests}{#1}%
  \setlength{\tabcolsep}{0mm}%
  \let\lp@orig@arraycr\@arraycr%
  \renewcommand{\@arraycr}{\lp@cr}%
  \renewcommand{\@currentlabel}{\p@lp@line\thelp@line}%
  \ifthenelse{%
    0=#1%
  }{%
    \def\lp@tab@format{{r@{~~~}>{$}l<{$}@{~~~~}l}}%
  }{%
    \def\lp@tab@format%
        {{r@{~~~}*{#1}{l}@{~}>{$}l<{$}@{~~~~}l@{~}*{#1}{r}}}
  }%
  %\center% <-- REMOVED
  \flushleft% <-- ADDED
  \expandafter\tabular\lp@tab@format%
  \lp@start@proof@line%
}{%
  \lp@stop@proof@line%
  \endtabular%
  %\endcenter% <-- REMOVED
  \endflushleft% <-- ADDED
  \setcounter{lp@total@nests}{0}%
  \ifthenelse{%
    0=\value{lp@nested}
  }{% All is well.
  }{% There are still open subproofs.
    \def\@currenvir{subproof}%
  }
}
\makeatother

\begin{document}
\noindent text
\begin{logicproof}{0}
    statement & justification
\end{logicproof}

\end{document}

Both solutions yield identical output: