# Fitch Natural Deduction with Beamer

I am building a presentation using Beamer and the Fitch Natural Deduction package by Selinger.

I am trying to use the \onslide command. For some reason it doesn't work when I follow the syntax and use a parenthesis afterwards {}, but if I just write it as is. Here is a code I found that works:

\documentclass[10pt,pdf]{beamer}

\usepackage{fitch}
\usepackage{amssymb}

\begin{document}

\begin{frame}
\frametitle {Working}

$\begin{nd} \have {1} {p \rightarrow q} \by {premise} {} \open \onslide<3-> \hypo {2} {\neg q} \open \onslide<5-> \hypo {3} {p} \onslide<6-> \have {a} {p \rightarrow q} \r{1} \onslide<7-> \have {4} {q} \ie{3,a} \onslide<8-> \have {5} {q \wedge \neg q} \ai{2,4} \onslide<9-> \have {6} {\bot} \close \onslide<4-> \have {8} {\neg p} \ni {3-6} \close \onslide<2-> \have {9} {\neg q \rightarrow \neg p} \pause \ii{2-8} \end{nd}$
\end{frame}

\end{document}


A problem I am facing is the inability to use the \onslide<+->, meaing with the plus sign. Meaning if I change the onslide from 6 onwards - it doesn't show the lines in the order I want to, meaing instead of: \onslide<6-> \have {a} {p \rightarrow q} \r{1}

write this: \onslide<+-> \have {a} {p \rightarrow q} \r{1}

and so on with 7, 8, 9 - when complied the order changes completely.

Note: In your example, I removed the call to \pause (what was it supposed to be used for)?

The <+> notation uses the beamerpauses counter (beamer user guide, p.90). To use this notation from 6th overlays, use \setcounter{beamerpause}{6}.

\documentclass[10pt,pdf]{beamer}
\usepackage{fitch}
\usepackage{amssymb}
\begin{document}
\begin{frame}
\frametitle {Working}

$\begin{nd} \onslide<1-> \have {1} {p \rightarrow q} \by {premise} {} \onslide<1-> \open \onslide<3-> \hypo {2} {\neg q} \onslide<3-> \open \onslide<4-> \hypo {3} {p} \onslide<5-> \have {a} {p \rightarrow q} \r{1} \setcounter{beamerpauses}{6} \onslide<+-> \have {4} {q} \ie{3,a} \onslide<+-> \have {5} {q \wedge \neg q} \ai{2,4} \onslide<+-> \have {6} {\bot} \onslide<+-> \close \onslide<4-> \have {8} {\neg p} \ni {3-6} \onslide<4-> \close \onslide<2-> \have {9} {\neg q \rightarrow \neg p} \ii{2-8} \end{nd}$
\end{frame}
\end{document}


• Thank you very much! The \pause command was there because I wanted to justification to appear after another click. Is there an option for that? Also, do you think there is a way line number 7 will appear after line number 3? The line with the \bot. Mar 19 at 15:04
• @Cantor You can adapt the overlay changes as you wish. Here I just show the use of the beamerpauses counter with +. Mar 19 at 15:24