I've written an introductory logic book in LaTeX and I want to have it in ConTeXt. I've made use of a .sty file (fitch.sty, authored by Peter Selinger, not distributed by TeXLive), downloadable here1. (I don't put the code here cause it has over 200 lines), and I'd like to make it work under ConTeXt, cause the use of graphic packages for making derivations is daunting. In a file called fitch.hacker.tex, Selinger says:
"The macros provided by this package mix TeX and LaTeX primitives. LaTeX is used for \rule, \settowidth, \addtolength, \hspace... All macros are assumed to be called in math mode."
If you try to compile fitch.sty with mkiv, you have only two error messages:
1) At lines
near the end of the file, and
2) At line 85:
I think error 1) is easily subsanable, I mean, to make it work under ConTexT is enough to define the pertinent commands. But I cannot figure out how to "translate" line 85 to ConTexT, cause \newlength is a macro that defines a length register. So:
¿Can anyone tell me if I'm right about error 1? ¿Can anyone tell me if exists a command or a script in ConTexT with the effect of \newlenght?