Relation pm#relation_from_relation_type (relation_type,*)
  supertype:  relation_from_type  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
  subtype:  relation_from_binary_relation_type (binary_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)
  subtype:  domain (relation_type,positive_integer,set_or_class)  the formula (sumo#domain ?REL ?INT ?CLASS) means that the ?INT'th element of each tuple in the relation ?REL must be an instance of ?CLASS
  subtype:  domain_subclass (relation_type,positive_integer,set_or_class)  the formula (sumo#domainSubclass ?REL ?INT ?CLASS) means that the ?INT'th element of each tuple in the relation ?REL must be a subclass of ?CLASS
  subtype:  range (function_type,set_or_class)  gives the range of a function, i.e. all of the values assigned by the function are instances of sumo#class
  subtype:  range_subclass (function_type,set_or_class)  all of the values assigned by the function in the 1st argument are subclasses of the 2nd argment
  subtype:  valence (relation_type,positive_integer)  specifies the number of arguments that a relation can take; if a relation does not have a fixed number of arguments, it does not have a valence and it is an instance of variable_arity_relation, e.g., sumo#holds is a variable_arity_relation
  subtype:  disjoint_relation (relation_type+)  (sumo#disjointRelation @ROW) means that any two relations in @ROW have no tuples in common; as a consequence, the intersection of all of the relations in @ROW is the null set
  subtype:  holds__hold (relation_type,*)  (holds P N1 ... NK) is true when the tuple of objects denoted by N1,..., NK is an element of the relation P
  subtype:  assignment_fn (function_type,*)  if F is a function with a value for the objects denoted by N1,..., NK, then (sumo#assignmentFn F N1 ... NK) is the value of applying F to the objects denoted by N1,..., NK; otherwise, the value is undefined
  subtype:  distributes__distribute (binary_function_type,binary_function_type)  a binary_function ?F1 is distributive over another binary_function ?F2 just in case (?F1 ?INST1 (?F2 ?INST2 ?INST3)) is equal to (?F2 (?F1 ?INST1 ?INST2) (?F1 ?INST1 ?INST3)), for all ?INST1, ?INST2, and ?INST3