Relation dl#subsumes_leaf__SBL (type,type)  the 2nd type is a leaf type subsumed by the 1st type
  supertype:  subtype__subtype_or_equal (pm)  subtype links should actually be strict subtype links or not much checking can be done
  subtype:  properly_subsumes_leaf__PSBL (type,type)  the 2nd type is a leaf type properly subsumed by the 1st type