Multi-choice impasses
---------------------

Multi-choice impasses arise when there is either a tie or conflict between
the candidate objects for a slot.  The default response to a multi-choice
impasse is to select the *selection* problem space, which provides operators
that *evaluate* the tied objects.  The selection space includes productions
that compare evaluations, and automatically translate them into preferences
for the various choices.  As soon as the selection space has generated
sufficient preferences to select one object amongst the choices, Soar selects
that object and terminates the multi-choice impasse.

The selection space might be rejected because it is not sufficient for
resolving the impasse, or because domain-dependent knowledge decides to
abandon it.  If the selection problem space is rejected for a multi-choice
impasse and no other problem space is selected, the impasse will be resolved
by creating additional preferences for the tied or conflicting objects.  If
the impasse was a tie, indifferent preferences will be created for all items
that tied, leading to a random selection.  If the impasse was a conflict, all
of the conflicting items are rejected.

The selection problem space is described in detail in Section *Note The
selection space for multi-choice impasses:: on page *Note The selection space
for multi-choice impasses::.