Built-in CAS Variables?

[Joe Horn]

Just being picky here: Those are constants, not vary-ables. The only CAS variables that I know of (they only work in CAS) are:

Digits -- the value in CAS Settings, page 1, end of line 2
epsilon -- the value in CAS Settings, page 2, line 4

Digits can be set to any integer 1 to 13 (13 shows as 12 in CAS Settings).

CAS doesn't like epsilon to be anything larger than 1E-6. If you set it to something larger than 1E-6, CAS will reset it to 1E-6.

Those two are the only CAS variables listed on this page: http://holyjoe.net/hp/PrimeVars.htm
If any more are discovered, I'll add them to that list.

The User Guide refers to "built-in CAS variables named a to z". That's incorrect. In CAS, a through z do not exist until you create them, and when you purge them, they no longer exist... just like any other user-created CAS variable. That's different from Digits and epsilon, which always exist and cannot be purged.