# fitch.sty LaTeX macros for Fitch style natural deduction ## Usage Fitch-style natural deduction is a system for writing proofs in propositional logic and predicate logic. This is a set of easy-to-use LaTeX macros originally written by Peter Selinger. It is used, e.g., in the various versions of _forall x_ by PD Magnus (e.g., the [original](https://www.fecundity.com/logic/download.html), [Cambridge](http://www.homepages.ucl.ac.uk/~uctytbu/OERs.html), and [Calgary](https://forallx.openlogicproject.org) versions) With these macros, one can typeset natural deduction proofs in Fitch style, as in the following example: ![](fitchexample.png) ``` \begin{nd} \hypo {1} {\forall y \neg P(y)} \open \hypo {2} {\exists x P(x)} \open[u] \hypo {3} {P(u)} \have {4}{\forall y \neg P(y)} \r{1} \have {5} {\neg P(u)} \Ae{4} \have {6} {\bot} \ne{3,5} \close \have {6a} {\bot} \Ee{2,3-6} \close \have {7} {\neg \exists x P(x)} \ni{2-6a} \end{nd} ``` The output is shown above, and the corresponding LaTeX code below. ## Changes **v0.6, Sept 4, 2023.** Updated the documentation and license (from GPL to LPPL). The code is essentially unchanged. **v0.5, Feb 8, 2005.** The ability to handle multi-line formulas was added. ## Download The package is available on CTAN as [`fitch`](https://ctan.org/pkg/fitch). The code is [maintained on Github](https://github.com/OpenLogicProject/fitch/). ## Related packages - The [`lplfitch`](https://ctan.org/pkg/lplfitch) packages produces Fitch-style roofs in the format used in Barwise & Etchemendy's textbook _Language, Proof, and Logic_. - The [`natded`](https://ctan.org/pkg/natded) package produces natural deduction roofs in the style of Jaśkowski, or that of Kalish and Montague. Additional packages for proofs, including Johan Klüwer's, are available at a [page maintained by Alex Kocurek](https://www.actual.world/latex/) ## People Peter Selinger, Dalhousie University, is the original author. Richard Zach, University of Calgary, it the current maintainer. ## License Copyright (C) 2002-2023 Peter Selinger This work may be distributed and/or modified under the conditions of the LaTeX Project Public License, either version 1.3 of this license or (at your option) any later version. The latest version of this license is in https://www.latex-project.org/lppl.txt and version 1.3c or later is part of all distributions of LaTeX version 2008 or later.