I was trying to change the math font used in plain TeX (as opposed to LaTeX or ConTeXt), but I didn’t seem to find it documented any where, apparently it is so obvious for TeXperts to be even documented. Anyway, I figured it out and I’m documenting it here so I don’t have to search it again.

Set font families 0-3 to the new font, as follows:

  • 0: math text (“sin”, “cos”, numbers, etc.)
  • 1: math italic (“x”, “y”, “z”, etc. don’t have to be italic at all e.g. Euler)
  • 2: math symbols
  • 3: math extensions
  • \textfont: normal size font
  • \scriptfont: font for sub/super script
  • \scriptscriptfont: font for subsub/supersuper script

Something like:

\textfont0              = \mathtext 
\scriptfont0            = \mathsubtext
\scriptscriptfont0      = \mathsubsubtext
\textfont1              = \mathlet
\scriptfont1            = \mathsublet
\scriptscriptfont1      = \mathsubsublet
\textfont2              = \mathsym
\scriptfont2            = \mathsubsym
\scriptscriptfont2      = \mathsubsubsym
\textfont3              = \mathext
\scriptfont3            = \mathsubext
\scriptscriptfont3      = \mathsubsubext