El 27.10.2017 a las 17:42, John Robert Hudson escribió:
I understand now; the undertilde package is no longer part of TeXLive but the undertilde character is provided by the wsuipa package
Yes. But the math manual referred to an accent while the wsuipa package only provides \undertilde as single character. So the note from JPierre is valid.
LyX supports the undertilde package natively as you can see in the document settings under "Math Options". I'll try to contact the author of the undertilde package to clarify the license.
regards Uwe
