Relation pm#quaternary_relation__quaternary_only_relation (?,?,?)  relation with a fixed arity equal to 4
  exclusion:  pm#binary_relation  pm#ternary_relation  pm#relation_with_variable_arity
  subtype:  kif#subst
  supertype:  pm#relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
     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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