Other no-change impasses
------------------------

The default response to a problem space or state no-change impasse is to do
nothing.  If a problem space can be selected in the subgoal, that implies
that there is domain-dependent knowledge to process the impasse.  However, if
one of these no-change impasses is followed by a goal no-change impasse, the
latter impasse indicates that there is *no* domain-dependent knowledge for
resolving the original problem space or state no-change.  When there is no
such knowledge, the default response is to abandon the current path.  The
minimal change that abandons the current path is to reject and reconsider the
most recently selected context object, which is the problem space or state on
which the original no-change impasse occurred.  For example, if there is a
state no-change followed by a goal no-change, the state will be rejected.