15.40.md

In the OrQuery eval function what would happen if its rhs member returned an empty set? What if its lhs member did so? What if both rhs and lhs returned empty sets?

If its rhs member returned an empty set, then the insert function would insert no element into the ret_lines.

If its lhs member returned an empty set, then the ret_lines would be initialized as an empty set.

If both rhs and lhs returned empty sets, then the ret_lines would also be an empty set.