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