[Tex/LaTex] customize description environment

descriptionenvironments

I would like to define an environment induction which is like the description environment. I have in mind that the output of

\begin{induction}{A}
\item[a1] Part $a1$ of the induction proof.
\item[a2] Part $a2$ of the induction proof. This one needs a further induction argument over $B$.
\begin{induction}{B}
\item[b1] Part $b1$ of the induction proof.
\end{induction}
\end{induction}

should be

\begin{enumerate}
\item[($A$-induction, $a1$)] Part $a1$ of the induction proof.
\item[($A$-induction, $a2$)] Part $a2$ of the induction proof. This one needs a further induction argument over $B$.
\begin{enumerate}
\item[($B$-induction, $b1$)] Part $b1$ of the induction proof.
\end{enumerate}
\end{enumerate}

I have tried to redefine \descriptionlabel but the way I did it I ran into trouble with nested induction environments.

Best Answer

Here is one possibility, by redefining the way \descriptionlabel works at the beginning of every induction environment:

enter image description here

\documentclass{article}

\newenvironment{induction}[1]
  {\renewcommand{\descriptionlabel}[1]{\hspace\labelsep\normalfont\bfseries$#1$-induction, $##1$}%
   \begin{description}}
  {\end{description}}
\begin{document}

\begin{induction}{A}
  \item[a1] Part~$a1$ of the induction proof.
  \item[a2] Part~$a2$ of the induction proof. This one needs a further induction argument over~$B$.
  \begin{induction}{B}
    \item[b1] Part~$b1$ of the induction proof.
  \end{induction}
\end{induction}

\end{document}

One thing I might change in your usage is to supply $A$ rather than A; that is, remove the automated math-mode insertion of the arguments to induction and \item.

The above solution re-uses the description environment within the induction environment. If you wish to mix the two, it's best to define induction to be completely separate from description:

enter image description here

\documentclass{article}

\providecommand*\inductionlabel{}

\makeatletter
\newenvironment{induction}[1]
  {\renewcommand{\inductionlabel}[1]{\hspace\labelsep\normalfont\bfseries$#1$-induction, $##1$}%
   \list{}{\labelwidth\z@ \itemindent-\leftmargin
          \let\makelabel\inductionlabel}}
  {\endlist}
\makeatother

\begin{document}

\begin{induction}{A}
  \item[a1] Part~$a1$ of the induction proof.
  \item[a2] Part~$a2$ of the induction proof. This one needs a further induction argument over~$B$.
  \begin{induction}{B}
    \item[b1] Part~$b1$ of the induction proof.
    \begin{description}
      \item[something] something else
    \end{description}
  \end{induction}
\end{induction}

\end{document}

Related Solutions

[Tex/LaTex] Dealing with long description environment items

Using the enumitem package with beamer is not a good idea; for example, just by loading enumitem, the default beamer font and color specifications for description are lost; moreover \setbeamercolor and \setbeamerfont will have no effect on description item; even worst, the enumitem package will also interfere with the beamer layout for itemize and enumerate; in fact, it will produce errors for the enumerate environment (See example at the bottom).

In the following example I defined a Ldescription environment based on the beamer definition of standard description; since the new definition follows the "beamer way", it will behave as expected (it's overaly aware, for exampe, and respects the color and font templates) and will give you the desired layout (feel free to adjust the lengths according to your needs):

\documentclass{beamer}
\usepackage{lipsum}

\makeatletter
\def\Ldescription{%
  \@ifnextchar[{\beamer@testforospec}{\beamer@descdefault\beamer@descriptionwidth\@@Ldescription}%
}

\def\beamer@testforospec[{\@ifnextchar<{\beamer@scandefaultospec[}{\@Ldescription[}}%

\def\beamer@scandefaultospec[#1]{\def\beamer@defaultospec{#1}\Ldescription}

\def\@Ldescription[#1]{%
\setbox\beamer@tempbox=\hbox{\def\insertdescriptionitem{#1}
  \usebeamertemplate**{description item}}%
\beamer@descdefault\wd\beamer@tempbox\@@description%
}%

\def\@@Ldescription{%
  \beamer@descdefault35pt%
  \list
  {}
  {\labelwidth\beamer@descdefault\leftmargin2.8em\let\makelabel\beamer@Ldescriptionitem}%
  \beamer@cramped%
  \raggedright
  \beamer@firstlineitemizeunskip%
}

\def\endLdescription{\ifhmode\unskip\fi\endlist}
\long\def\beamer@Ldescriptionitem#1{%
  \def\insertdescriptionitem{#1}%
  \hspace\labelsep{\parbox[b]{\dimexpr\textwidth-\labelsep\relax}{%
        \usebeamertemplate**{description item}%
    }}}
\makeatother

\begin{document}

\begin{frame}
\begin{Ldescription}
\item<1->[very very very very long item] \lipsum[2]
\item<2,4>[short titem] description 2
\item<3->[another very very very very long item] description 3
\item<4->[short item] description 4
\end{Ldescription}
\end{frame}

\end{document}

An image of the fourth frame:

enter image description here

Why enumitem shouln't be used with beamer

Processing the following code:

\documentclass{beamer}
%\usepackage{enumitem}

\setbeamercolor{description item}{fg=olive!80!black}
\setbeamerfont{description item}{size=\footnotesize}

\begin{document}

\begin{frame}
\begin{description}
\item[item] description
\end{description}
\begin{itemize}
\item description
\end{itemize}
\end{frame}

\end{document}

produces the following (expected) output:

enter image description here

Now uncomment-out the line loading enumitem. reprocess and now you'll get the following undesired result:

enter image description here

Now, try this simple document:

\documentclass{beamer}
\usepackage{enumitem}

\begin{document}

\begin{frame}
\begin{enumerate}
\item test
\end{enumerate}
\end{frame}

\end{document}

and you'll receive:

! TeX capacity exceeded, sorry [grouping levels=255].
\labelenumi ->{
               \labelenumi }
l.10 \end{frame}
                
!  ==> Fatal error occurred, no output PDF file produced!

The moral is clear: enumitem and beamera are incompatible. Perhaps using the loadonly package option to create own lists could be safe:

\usepackage[loadonly]{enumitem}

[Tex/LaTex] Line break after description label

The insertion of an empty item seems to give a better vertical spacing. One can define a myitemize environment that includes this empty item; that will prevent typing it for each description item:

\documentclass{article}

\usepackage{enumitem}

\newenvironment{myitemize}%
{\begin{itemize}\item[]}
{\end{itemize}}

\begin{document}

\begin{description}[style = sameline, leftmargin = 1em]
\item[Animals:]
  \begin{itemize}
  \item[]
  \item Dog
  \item Cat
  \item Fish
  \end{itemize}

\item[Colors:]
  \begin{myitemize}
  \item Red
  \item Green
  \item Blue
  \end{myitemize}
\end{description}

\end{document}

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] Dealing with long description environment items

Why enumitem shouln't be used with beamer

[Tex/LaTex] Line break after description label

Related Question