am* fonts are being removed from everything except the TeXbook
source and the associated manmac.tex.  If you want to try out
your version of TeX on the TeXbook manuscript, you will have
to reload a special version of TeX with am_plain.tex.  You will
not, of course, be able to print the results, but you are not
supposed to be doing that anyway.  The source of the TeXbook is
included as a model for the construction of certain types of
macro, not as user documentation.
