Question about temporary variables



I know that sometimes in the solving code (esp. Barton's stuff) we can
get temporary integer or real or whatever variables that look like i3
or r55.

But what the heck are the g things here?   This comes from Sage ticket
http://trac.sagemath.org/sage_trac/ticket/9825

x1(t)=ilt(-((3*laplace(x2(t)^2,t,?g1811)-x1(0))*?g1811-3)/?g1811^2,?g1811,t)

This comes from a desolve command, but tracking down exactly what Sage
has sent to Maxima to get this would be tedious.  Needless to say,
trying to search the manuals for this wasn't so helpful, e.g.
http://maxima.sourceforge.net/docs/manual/en/maxima_22.html has
examples that work, not ones that don't.

But we'd be grateful for the help so we can properly parse Maxima
answers even more accurately.  Thanks!