Relation pm#relation_to_class (*,rdfs#class)
  subtype:  pm#kind  sumo#extension_fn
  supertype:  pm#relation_to_set_or_class (*,pm#set_or_class)
     supertype:  pm#relation_to_collection (*,pm#collection)
        supertype:  pm#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:  pm#relation__related_thing__relatedthing___related_with (*)  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
        supertype:  pm#what_relation (*)
           supertype:  pm#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 
              supertype:  pm#relation__related_thing__relatedthing___related_with (*)  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
  supertype:  pm#relation_to_type (*,pm#type)
     supertype:  pm#relation_to_collection (*,pm#collection)


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