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