Function pm#complement_type (pm#type -> pm#type)  a supertype of owl#complement_of which can only connect RDFS/OWL classes
  supertype:  pm#closed_exclusion  the '/' link in the FT notation:  the two linked types either are respectively identical to pm#thing and pm#nothing (they are "complement types") or they subtype a same type and form a complete subtype partition
  subtype:  pm#complement_class (rdfs#class -> rdfs#class)  if something is not in one of the classes, then it is in the other, and vice versa; in WebKB, use the link '/'