some PDFs do not render because feed expressions contain underscore

[researcherben]

There's a design flaw in how feeds are implemented in .tex files. See, for example, derivation 282755 (radius for satellite in geostationary orbit) step ID = 2499406:

\dividebothsidesby{\frac{m_{\rm satellite}}{r}}{4948724}{2009493}

Because the feed expression contains an underscore, the macro doesn't get parsed correctly.

This poor handling of strings is a recurring theme; see https://github.com/allofphysicsgraph/proofofconcept/issues/267 and https://github.com/allofphysicsgraph/proofofconcept/issues/249. I wasn't careful about how Latex strings get used.