# Any good way to write mathematical induction proof steps in LaTeX?

I need to write some mathematical induction using LaTeX. Are there any packages that I can use for that purpose?

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I think this is a work for the alignat. Some comments about the code:

• The package enumitem provides the label key which I have used to modify the label for the inner itemize environment.

• I have manually added some space (v. \medskip in the code) so that the output resembles the scan copy.

\documentclass{amsart} % http://www.ctan.org/pkg/amsart
\usepackage{enumitem}  % http://www.ctan.org/pkg/enumitem
\begin{document}
\begin{itemize}
\item \emph{Induction Principle}: The formula $\phi$ may be derived by proving the formula \medskip
\begin{itemize}[label=$\lozenge$, itemsep=2ex]
\item \emph{Base Case}:
$\texttt{(implies (and (not }q_1 \texttt{)} \dots \texttt{(not }q_k\texttt{)) }\phi\texttt{)}$
\item \emph{Induction Step(s)}: For each $1 \leq i \leq n$,
\begin{alignat*}{5}
&&     &              &&      &&\phi/\sigma_{i,1}\\
&&     &              &&      &&\dots\\
&&     &              &&      &&\phi/\sigma_{i,k_i}\texttt{)} \\
&&     &\phi\texttt{)}
\end{alignat*}
provided that for terms $m, q_1, \dots, q_k$, and substitutions $\sigma_{i,j}$ ($1 \leq i \leq h_i$), the following measure conjectures are theorems.
\item \texttt{(EO-ORDINALP} $m$\texttt{)}
\item For each $1 \leq i \leq k$ and for $1 \leq j \leq h_i$,
$\texttt{(IMPLIES } q_i \texttt{ (EO-ORD-< } m/\sigma_{i,j} \quad m \texttt{))}$
\end{itemize}
\end{itemize}
\end{document}


Thanks to egreg who has kindly gifted me these and agreed not to steal my green tick, I have learnt atleast two different ways of doing this:

• a quick reference for tabbing could be this one.

• There is one other important fact that he told me here: If a minipage contains only a tabbing environment, the minimum of width of the tabbing environment and the specified width would be the width of the minipage.

The Code Snippets

$% works without \[ and$ as well.
\begin{minipage}{\linewidth}
\begin{tabbing}
\texttt{(implies}\quad\= \texttt{(and}\quad\= $q_i$ \\
\>                   \> $\phi/\sigma_{i,1}$\\
\>                   \> \dots\\
\>                   \>  $\phi/\sigma_{i,k_i}$\texttt{)} \\
\> $\phi$\texttt{)}
\end{tabbing}
\end{minipage}
\]

$% works without \[ and$ as well.
\begin{minipage}{\linewidth}\ttfamily
\begin{tabbing}
(implies\quad\= (and\quad\= $q_i$ \\
\>          \> $\phi/\sigma_{i,1}$\\
\>          \> \dots\\
\>          \>  $\phi/\sigma_{i,k_i}$) \\
\> $\phi$)
\end{tabbing}
\end{minipage}
\]


Please note that, I have added the comment:

 % works without $and$ as well.


to bring to the fore that, you may therefore align this to the left, as in the scan by dropping the $...$.

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What I do is just to use a description environment, with Base: and Induction: labels.

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