Relation sumo#subclass__subclass_of (sumo#set_or_class,sumo#set_or_class)  if the common reading conventions of parameters had been respected, this type would have been named subclass_of; every instance of the 1st argument is also an instance of the 2nd argument; a class may have multiple superclasses and subclasses
  supertype:  pm#subclass_of_or_equal (pm)  pm#partial_ordering_relation (pm)
  instance of:  pm#binary_predicate_type (pm)  pm#partial_ordering_relation_type (pm)
  subtype:  sumo#immediate_subclass__immediate_subclass_of (sumo#set_or_class,sumo#set_or_class)  the 1st argument is a subclass of the 2nd argument and there is no other subclass of the 2nd argument such that the 1st is also a subclass of the 2nd; in WebKB, use the link '<'