Relation pm#object_relation (?,?)
  exclusion:  attributive_relation  mereological_relation  intentional_relation  temporal_relation
  subtype:  object  domain_object
  supertype:  relation_playing_a_special_role (*)  this type permits to categorize relations according to their roles ; this is a traditional but quite subjective 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