How to make fonts bigger in **plain tex** math mode?

[Ulrike Fischer]

Am Fri, 28 Apr 2023 10:28:32 +0100 schrieb Philip Taylor (Hellenic
Institute):

>> When I ran your code under luatex, here's what happened:
 
> Sorry, Steve, you originally wrote "How do I make fonts bigger in 
> **plain tex** math mode", not "[...] in **plain LuaTeX** [...]". Had I 
> known that you were using LuaTeX I would not even have tried to answer 
> your question as I never use LuaTeX simply /because/ it is not 
> compatible with TeX /qua/ TeX.

Well your code doesn't work with pdftex (or xelatex) neither. 

You introduced U+A0 (no break spaces) after some of the fontnames,
and now TeX is looking e.g. for cmr7U+A0 and is a bit unhappy.

If I remove all no break space the code compiles both with luatex
and pdftex.

-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/