Relation rdfs#sub_class_of__subclassof__super_class__superclas (class,class)  in WebKB, use the link '<'
  equal:  sub_class_of
  supertype:  relation_to_another_class (class,class+)
     supertype:  relation_from_class_to_collection (class,collection)
        supertype:  relation_from_type_to_collection (type,collection)
           supertype:  relation_between_collections (collection,collection+)
              supertype:  relation_from_collection (collection,*)
                 supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
                    >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
                 supertype:  what_relation (*)
                    supertype:  wh-/how_relation (*)  this type permits to categorize relations according to the usual who/what/why/where/when/how questions ; this is a traditional but very subjective and ineffective way of categorizing relations 
                       >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
              supertype:  relation_to_collection (*,collection)
                 supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
                 supertype:  what_relation (*)
           supertype:  relation_from_type (type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
              supertype:  relation_from_collection (collection,*)
        supertype:  relation_from_class (class,*)
           supertype:  relation_from_type (type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
     supertype:  relation_to_another_set_or_class (set_or_class,set_or_class+)  this category is needed to group SUMO relations between classes which cannot be subtype of pm#relation_from_type because their signatures curiously also involve sets
        supertype:  relation_between_collections (collection,collection+)
        supertype:  relation_to_set_or_class (*,set_or_class)
           supertype:  relation_to_collection (*,collection)
  supertype:  subclass_of_or_equal (set_or_class,set_or_class)
     supertype:  relation_to_another_set_or_class (set_or_class,set_or_class+)  this category is needed to group SUMO relations between classes which cannot be subtype of pm#relation_from_type because their signatures curiously also involve sets
  supertype:  supertype (type,type)  in the FT notation, the '<' link is only used to connect to a "strict" supertype
     supertype:  relation_from_type (type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
     supertype:  generalizing_type (?,type)  fuzzy category, DO NOT USE DIRECTLY
        supertype:  partial_ordering_relation (?,?)  this category only serves structuration purposes: it is instance of pm#partial_ordering_relation_type which is not instance of pm#class_of_inheritable_relation_type
           supertype:  reflexive_relation__reflexiverelation (?,?)  this category only serves structuration purposes: it is instance of pm#reflexive_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 (?,?)
           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 (?,?)