Relation pm#exclusive_class__exclusiveclas (class,class)  the 2 classes have no common subtype/instance; in WebKB, use the link '!'
  supertype:  relation_to_another_class  disjoint  exclusive_type  different
  equal:  disjoint_with (pm)
  subtype:  complement_class (class -> class)  if something is not in one of the classes, then it is in the other, and vice versa; in WebKB, use the link '/'