Relation sumo#identity_element (?,?)
  type:  binary_predicate_type  the class of predicates relating two items - its valence is two
  type:  asymmetric_relation_type  an antisymmetric and irreflexive relation
  supertype:  asymmetric_relation (?,?)  this category only serves structuration purposes: it is instance of pm#asymmetric_relation_type which is not instance of pm#class_of_inheritable_relation_type
     supertype:  irreflexive_relation__irreflexiverelation (?,?)  this category only serves structuration purposes: it is instance of pm#irreflexive_relation_type which is not instance of pm#class_of_inheritable_relation_type
        supertype:  binary_relation_with_particular_mathematical_property (?,?)
           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
     supertype:  antisymmetric_relation__antisymmetricrelation (?,?)  this category only serves structuration purposes: it is instance of pm#antisymmetric_relation_type which is not instance of pm#class_of_inheritable_relation_type
        supertype:  binary_relation_with_particular_mathematical_property (?,?)