I'm trying to export a PDF of a LyX document (it has never caused a problem before). Below I have posted pictures of the error message along with the equation LyX highlighted for me. I don't know what
\hbox is, and I didn't use that in my code. Can someone please help me edit the equation so that I can export a PDF?
\coloneqqis unknown, you need to load a package for this, such as
Add to your document preamble:
LyX 2.1 will have direct