Relation pm#equal (?,?)  "=" in KIF; true if the 1st argument is identical to the 2nd
  exclusion:  different
  subtype:  same_as  MORE PRECISE TYPES THAN THIS ONE SHOULD BE USED
  equal:  equal (pm)
  type:  binary_predicate_type  the class of predicates relating two items - its valence is two
  type:  equivalence_relation_type  binary_relation that is reflexive, symmetric and transitive
  type:  type_of_relation_extended_to_quantities  relation that, when it is true on a sequence of arguments that are real_numbers, it is also true on a sequence of constant_quantites with those magnitudes in some unit of measure; for example, the less_than relation is extended to quantities; this means that for all pairs of quantities ?q1 and ?q2, [?q1,  sumo#less_than: ?q2] if and only if, for some numbers ?n1 and ?n2 and unit ?u, [q1 =  sumo#measure_fn(?n1,?u)], [q2 =  sumo#measure_fn(?n2,?u)] and [?n1, less_than: ?n2] for all units on which ?q1 and ?q2 can be measured; note that, when a relation_extended_to_quantities is extended from real_numbers to constant_quantities, the constant_quantities must be measured along the same physical dimension
  supertype:  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
     supertype:  reflexive_relation__reflexiverelation (?,?)  this category only serves structuration purposes: it is instance of pm#reflexive_relation_type which is not instance of pm#class_of_inheritable_relation_type
        supertype:  binary_relation_with_particular_mathematical_property (?,?)
           supertype:  relation_with_particular_mathematical_property (*)
              supertype:  relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
                 >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
     supertype:  symmetric_relation__symmetricrelation (?,?)  this category only serves structuration purposes: it is instance of pm#symmetric_relation_type which is not instance of pm#class_of_inheritable_relation_type
        supertype:  binary_relation_with_particular_mathematical_property (?,?)
     supertype:  transitive_relation (?,?)  this category only serves structuration purposes: it is instance of pm#transitive_relation_type which is not instance of pm#class_of_inheritable_relation_type
        supertype:  binary_relation_with_particular_mathematical_property (?,?)