🚀 go-pugleaf

I've been using AMS-LaTeX, which is lovely, except that it takes a while
to load up all the style files it uses before it ever looks at my TeXfile.

To speed things up, I tried to generate a format file that had the amsppt
documentstyle preloaded.  I added the line
   \documentstyle{amsppt}
to the end of lplain.tex, after the line
   \typeout{Input any local modifications here.}
but I get the following error message:

Input any local modifications here.
(amsppt.sty version 2.1a (22-JAN-1992): Loading utility definitions,
! Undefined control sequence.
l.66 \Invalid@
              \usualspace
?

Does anyone know what's wrong?  In any case, how do you preload amsppt
(along with all the things that amsppt.sty inputs)?

Thanks in advance,
Phil Hirschhorn
phirschhorn@lucy.wellesley.edu