Relation pm#binary_relation (?,?)  in WebKB, most relation types are binary and some have a variable number of arguments (as in KIF), hence this type is currently only specialized by types that I do not want to see as direct subtypes of pm#relation
  exclusion:  pm#ternary_relation  pm#quaternary_relation  pm#relation_with_variable_arity
  subtype:  pm#unary_function  dc#Relation {dc#Type dc#Description}  pm#relation_from_or_to_WordNet_type  nsm#before  nsm#after
  type:  pm#binary_relation_type  all binary relation types are instance of that object
  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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