gpg -o doc.gpg --symmetric doc
gpg -o doc -d doc.gpg # if you don't specify '-o ...' it will go to stdout

Makefile

.PHONY: test.pdf test.dvi fonts

test.pdf: test.dvi
	dvipdfmx $<
	mv $@ /tex_tmp/
	rm $< test.log
	evince /tex_tmp/$@

test.dvi: test.tex
	tex \\let\\pdf+ \\input $<

fonts:
	echo cmtt10 | tex \\input testfont \\table \\end
	dvipdfmx testfont.dvi
	mv testfont.pdf /tex_tmp/cmtt.pdf
	echo cmr10 | tex \\input testfont \\table \\end
	dvipdfmx testfont.dvi
	rm testfont.dvi testfont.log
	mv testfont.pdf /tex_tmp/cmr.pdf
	evince /tex_tmp/cmr.pdf /tex_tmp/cmtt.pdf

TeX example

Understand how this works:
\vbox{
\def\1{\vrule height 0pt depth 2pt}
\def\2{\vrule height 0pt depth 4pt}
\def\3{\vrule height 0pt depth 6pt}
\def\4{\vrule height 0pt depth 8pt}
\def\ruler#1#2#3{\leftline{$\vcenter{\hrule\hbox{\4#1}}\,\,\rm#2\,{#3}$}}
\def\\#1{\hbox to .125in{\hfil#1}}
\def\8{\\\1\\\2\\\1\\\3\\\1\\\2\\\1\\\4}
\ruler{\8\8\8\8}4{in}}
\end

Set theory axioms.
Construct models for set theory.
Don't work with sentences, work with models.
Read Paul Cohen - Set Theory and the Continuum Hypothesis.

For explanation of LANG vs. LC_ALL vs. LC_CTYPE see https://www.tug.org/TUGboat/tb19-3/tb60bzyl.pdf

Double quotes in TeX

\lq{}\lq\lq\ = \rq\thinspace\rq\rq
\lq\lq\thinspace\lq\ = \rq\rq{}\rq\ = \rq\rq\rq

Run
  tftopl cmr10.tfm cmr10.pl
and in cmr10.pl see KRN and other stuff for characters '42, '47, '140, '134 to understand why spaces after different types of quotes are the way they are. (\lq\lq and \rq\rq form ligatures)

Run this to understand what those numbers mean:
\obeylines
\char'42
\char'47
...
\bye

-----------

To understand how tfm files work, do this:

change something in cmr10.pl, for example in "(LABEL C v)", then generate new cmr10.tfm, then
use this test.tex:

\showboxbreadth \maxdimen
\showboxdepth \maxdimen
\setbox0=\hbox{va}
\showbox0
\bye

and see log file to check how those change worked

TeX QUESTIONS

* Is empty control sequence (\csname\endcsname) of any practical use at all? (see example about empty control sequence in http://tug.org/TUGboat/tb35-1/tb109knut.pdf)
* For what reason \lowercase{} and \uppercase{} is done a savoir in stomach and not in mouth?