Relation sumo#conclusion ()
  type:  pm#binary_predicate_type  the class of predicates relating two items - its valence is two
  type:  pm#single_valued_relation_type  when an assignment of values to every argument position except the last one determines at most one assignment for the last argument position; not all single_valued_relations are total_valued_relations
  type:  pm#total_valued_relation_type  when there exists an assignment for the last argument position of the relation given any assignment of values to every argument position except the last one; note that declaring a relation to be both a total_valued_relation and a single_valued_relation means that it is a total function