Relation pm#object_in_domain_of_object (pm#thing_that_is_not_a_domain,pm#thing_that_is_not_a_domain)  all relations non exclusive with this one are subtypes of this one; this is stated via:
              pm#relation subtype: {(pm#object_in_domain_of_object  pm#relation_from_a_domain pm#object_subdomain)};
  type:  pm#virtual_relation_type
  supertype:  pm#relation_from_a_thing_that_is_not_a_domain__thing_in_domain_of_object (pm#thing_that_is_not_a_domain,?)
     supertype:  pm#domain_related_relation__domain-related-thing (?,?)
        supertype:  pm#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
           supertype:  pm#relation__related_thing__relatedthing___related_with (*)  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type


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