Relation pm#relation_with_particular_mathematical_property (*)
  subtype:  pm#binary_relation_with_particular_mathematical_property
  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
     >part of:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type