Relation pm#binary_relation_with_particular_mathematical_property (?,?)
  subtype:  injective_binary_relation  trichotomizing_relation  reflexive_relation  irreflexive_relation  symmetric_relation  antisymmetric_relation  transitive_relation  intransitive_relation
  supertype:  relation_with_particular_mathematical_property (*)
     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