Relation pm#relation_from_binary_relation_type (binary_relation_type,*)
  supertype:  relation_from_relation_type
  subtype:  relation_to_another_binary_relation_type (binary_relation_type,binary_relation_type)
     subtype:  equivalent_property (binary_relation_type,binary_relation_type)  in WebKB, use the link '='
     subtype:  sub_property_of (binary_relation_type,binary_relation_type)  in WebKB, use the link '<'
     subtype:  inverse__reverse (binary_relation_type -> 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 '-'
  subtype:  domain (binary_relation_type,class)
  subtype:  range (binary_relation_type,class)