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:  ternary_relation  quaternary_relation  relation_with_variable_arity
  subtype:  unary_function  Relation {Type Description}  relation_from_or_to_WordNet_type  before  after
  type:  binary_relation_type  all binary relation types are instance of that object
  supertype:  relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
     >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type