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, Cambridge, and Calgary versions)

With these macros, one can typeset natural deduction proofs in Fitch style, as in the following example:

\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.

The code is maintained on Github.

Related packages

• The lplfitch packages produces Fitch-style roofs in the format used in Barwise & Etchemendy's textbook Language, Proof, and Logic.
• The 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

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.