Relation sumo#sister (?,?)
  type:  irreflexive_relation_type  r is irreflexive if r(?i,?i) holds for no value of ?i
  type:  transitive_relation_type  a binary_relation ?REL is transitive if (?REL ?INST1 ?INST2) and (?REL ?INST2 ?INST3) imply (?REL ?INST1 ?INST3), for all ?INST1, ?INST2, and ?INST3
  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:  transitive_relation (?,?)  this category only serves structuration purposes: it is instance of pm#transitive_relation_type which is not instance of pm#class_of_inheritable_relation_type
     supertype:  binary_relation_with_particular_mathematical_property (?,?)