Relation pm#equal (?,?)  "=" in KIF; true if the 1st argument is identical to the 2nd
  exclusion:  pm#different
  supertype:  pm#equivalence_relation__equivalencerelation  this category only serves structuration purposes: it is instance of pm#equivalence_relation_type which is not instance of pm#class_of_inheritable_relation_type
  instance of:  pm#binary_predicate_type  pm#equivalence_relation_type  pm#type_of_relation_extended_to_quantities
  equal:  sumo#equal (pm)
  subtype:  owl#same_as (?,?)  MORE PRECISE TYPES THAN THIS ONE SHOULD BE USED
     subtype:  pm#same_type_as (pm#type,pm#type)
        subtype:  owl#equivalent_class (rdfs#class,rdfs#class)  in WebKB, use the link '='
        subtype:  owl#equivalent_property (pm#binary_relation_type,pm#binary_relation_type)  in WebKB, use the link '='
     subtype:  owl#same_individual_as (?,?)