Weird CAS Vars

[Helge Gabert]

I recently noticed that some weird matrices appeared in the matrix editor, and in the memory manager (under CAS Vars), e.g., `_1101214768`, `_650534198`, etc. They all consist of one element, DOM SYMBOLIC.

In addition, a c__0 matrix appeared, consisting of DOM SYMBOLIC, [line[0,+infinity]], [].

I'm wondering if these variables can be safely deleted (perhaps intermediate garbage collection wasn't performed), or if this indicates some kind of system instability.