The file detex.el is for GNU emacs, and will provide the commands M-x detex and M-x delatex if it is loaded into a TeX-mode session. The file tex-start.ml is for use by TeX82 (see man page) to allow switching to Gosling's Emacs at a line number given on the command line Put tex-start.ml in /usr/lib/tex if you want to use Gosling emacs. The default editor line in site.h calls on GNU emacs, so you should edit this to put in the line emacs -ltex-start -estartline %s %d if you want Gosling (Unipress) Emacs.