Relation pm#relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
  subtype:  relation_with_particular_mathematical_property {binary_relation ternary_relation quaternary_relation relation_with_variable_arity}  relation_using_a_world_as_argument  relationship  class_of_relationship  class_of_class_of_relationship
  >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type