zeroa (zero+infinitesimal) and zerob (zero-infinitesimal)
are not documented, but they are $-symbols, and thus
available to the user.
They should either be documented, or made into internal
symbols. If they are documented, they need to be
Most parts of Maxima don't know about zeroa on input,
and as far as I know, no part of Maxima uses zeroa for
user output (but see bug 774065), so I would suggest
making them internal. The symbols zeroa and zerob
(without dollarsign) are currently used only in defint.lisp
(ask-greateq), and that appears to be a bug.