Relation pm#subclass_of_or_equal (set_or_class,set_or_class)
  subtype:  subclass  sub_class_of
  supertype:  relation_to_another_set_or_class (set_or_class,set_or_class+)  this category is needed to group SUMO relations between classes which cannot be subtype of pm#relation_from_type because their signatures curiously also involve sets
     supertype:  relation_between_collections (collection,collection+)
        supertype:  relation_from_collection (collection,*)
           supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
              >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
           supertype:  what_relation (*)
              supertype:  wh-/how_relation (*)  this type permits to categorize relations according to the usual who/what/why/where/when/how questions ; this is a traditional but very subjective and ineffective way of categorizing relations 
                 >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
        supertype:  relation_to_collection (*,collection)
           supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
           supertype:  what_relation (*)
     supertype:  relation_to_set_or_class (*,set_or_class)
        supertype:  relation_to_collection (*,collection)