4. Tree proofs

A non-closing tree

The task is to set proof-trees in the style of the tree alongside, i.e. tableaux of the sort that appear in e.g. Richard Jeffrey’s classic Formal Logic or my own Introduction to Formal Logic. Despite the very wide use of such tableaux, there has only lately appeared a purpose-designed package which looks excellent and very flexible, allowing you also to add line numbers (if you want) and line-by-line justifications:

Older options for setting tableaux often required bits of trickery to get nice-looking trees (and didn’t supply the option of line numbers etc.).  I’ll mention them, however, in case they may be enough for your purposes.

  • The illustration above was set using the pst-tree package which is part of the powerful pstricks family of packages which you may already know. But this can be a little cumbersome to use, e.g. to fine-tune the placing of the diagonal lines.
  • The qtree.sty package (Jeff Siskind and Alexis Dimitriadis) was written for typesetting linguists’ syntactic trees, and can also be adapted to logicians’ purposes. There is a useful tutorial for using qtree for logic here: LaTeX and tableaux (Charles Pence)
  • Another package originally written for linguists is synttree, which has a pleasing simple syntax in use (Matijs van Zuijlen).
  • pgf and TikZ (Till Tantau 2005-: a general TeX macro package for generating graphics, with a user-friendly syntax layer called TikZ). tikz-qtree provides a macro for drawing trees with TikZ using the easy syntax of qtree.
  • Then there is forest (Sašo Ži­vanović, 2012–2017). This is another package that  pro­vides PGF/TikZ-based apparatus for draw­ing trees, and looks very flexible. There is a nice worked example in the first answer here which shows how to fine-tune the output.

Clea Rees’s prooftrees package is based on forest. Here’s a fully annotated tree produced by this package:

Screengrab copy

See my document for more examples.

Links checked 12 February 2017

4 Responses to 4. Tree proofs

  1. Clea F. Rees says:

    Note that prooftrees CAN now be used with bussproofs. Either load bussproofs first. Or load prooftrees with option ‘tableaux’: ‘\usepackage[tableaux]{prooftrees}’. Either way, you can then use ‘prooftree’ for bussproofs trees and ‘tableau’ for prooftrees trees. Take care not to load the tableaux package instead which, as far as I can tell, does something completely different. The tableaux package is loaded with ‘\usepackage{tableau}`. However, should you need bussproofs, tableaux and prooftrees in the same document, I *think* it should still all play nicely together, as tableaux does not seem to define a ‘tableau’ environment, but only provides a ‘tableau’ .sty file. It would help a bit if package authors didn’t commandeer not one, but multiple names – if bussproofs provided ‘bussproof’, say! In the beginning, package authors believed names would always be plentiful and life simple and good. By now, of course, life is no longer so simple.

  2. Clea F. Rees says:

    You don’t need to hard code the line references, by the way.

  3. Jan von Plato says:

    Rather than “illustrated tree” one could write “annotated tree,” that’s the linguists’ term for syntax trees with nodes annotated by expressions.

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