🚀 go-pugleaf

(I suspect that my mail won't get through to Pierre's address, so I
post.)

The TeXbook indexes "\font", which is the current font.  At the
primitive level, fonts are manipulated using \font.

Defining \ninerm as a switch to the CM 9pt roman font:

    \font\ninerm=cmr9   % TeXbook, p 16

The current font is denoted by \font.  In the above context, both of
the following two lines expand to "cmr9":

    \fontname\font     % p 213
    \fontname\ninerm   % same paragraph

Equality of font control sequences can be tested.  Now, what I don't
know is whether that should be the simpler looking:

    \ifx\font\ninerm ... \else ... \fi    % p 210, top paragraph

OR (trying to read b/w Knuth's lines):

    \ifx\the\font\ninerm ... \else ... \fi    % p 214, last paragraph

If anyone reading this would like to write a textbook more clearly
than Knuth, may I suggest MORE EXAMPLES ?  Knuth tries to do too much
at once, as research-minded people often do, but this is no way to
teach.  Let's remember that teaching a new subject means that the
students are learning it for the FIRST time.

All the Best!
Geoffrey Tobin