Relation pm#relation_to_another_binary_relation_type (pm#binary_relation_type,pm#binary_relation_type)
  supertype:  pm#relation_from_binary_relation_type
  subtype:  owl#equivalent_property (pm#binary_relation_type,pm#binary_relation_type)  in WebKB, use the link '='
  subtype:  rdfs#sub_property_of (pm#binary_relation_type,pm#binary_relation_type)  in WebKB, use the link '<'
  subtype:  pm#inverse__reverse (pm#binary_relation_type -> pm#binary_relation_type)  for inverseOf(R,S) read: R is the inverse of S; i.e. if R(x,y) then S(y,x) and vice versa; in WebKB, use the link '-'