Relationpm#relation__related_thing__relatedthing___related_with(*)type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_typesubtype: pm#relation_from/to_thing_of_common_kind pm#relation_playing_a_special_role pm#wh-/how_relation pm#relation_with_particular_property type: pm#relation_typethere are three kinds of relation(_types): pm#predicate_type, pm#function_type and sumo#list; both predicates and functions denote sets of ordered n-tuples; the difference between these two classes is that predicates cover formula-forming operators, while functions cover term-forming operators; a list, on the other hand, is a particular ordered n-tuple