Relation pm#relation_to_set_or_class (*,set_or_class)
  supertype:  relation_to_collection
  subtype:  closed_on (function_type,set_or_class)  a binary_function is closed on a set_or_class if it is defined for all instances of the set_or_class and its value is always an instance of the set_or_class
  subtype:  reflexive_on__reflexiveon (binary_relation_type,set_or_class)  a binary_relation is reflexive on a set_or_class only if every instance of the set_or_class bears the relation to itself
  subtype:  irreflexive_on__irreflexiveon (binary_relation_type,set_or_class)  a binary_relation is irreflexive on a set_or_class only if no instance of the set_or_class bears the relation to itself
  subtype:  partial_ordering_on (binary_relation_type,set_or_class)  a binary_relation is a partial ordering on a set_or_class only if the relation is reflexive_on the set_or_class, and it is both an antisymmetric_relation, and a transitive_relation
  subtype:  total_ordering_on (binary_relation_type,set_or_class)  a binary_relation ?REL is a total ordering on a set_or_class only if it is a partial ordering for which either (?REL ?INST1 ?INST2) or (?REL ?INST2 ?INST1) for every ?INST1 and ?INST2 in the set_or_class
  subtype:  trichotomizing_on (binary_relation_type,set_or_class)
  subtype:  equivalence_relation_on (binary_relation_type,set_or_class)  a binary_relation is an equivalence_relation_on a set_or_class only if the relation is reflexive_on the set_or_class and it is both a transitive_relation and a symmetric_relation
  subtype:  relation_to_class (*,class)
     subtype:  kind__type___class___instance_of__instanceof (?,class)  the '^' link in the FT notation
     subtype:  extension_fn__extensionfn (Attribute -> class)  a unary_function that maps an attribute into the class whose condition for membership is the attribute
  subtype:  relation_to_another_set_or_class (set_or_class,set_or_class+)  this category is needed to group SUMO relations between classes which cannot be subtype of pm#relation_from_type because their signatures curiously also involve sets
     subtype:  disjoint (set_or_class,set_or_class)  like sumo#disjoint but from a a pm#set_or_class to another
        subtype:  disjoint (set_or_class,set_or_class)  classes are exclusive/disjoint only if they share no instance (and hence no subtype), i.e. just in case the result of applying sumo#intersection_fn to them is empty
        subtype:  exclusive_class__exclusiveclas (class,class)  the 2 classes have no common subtype/instance; in WebKB, use the link '!'
           subtype:  complement_class (class -> class)  if something is not in one of the classes, then it is in the other, and vice versa; in WebKB, use the link '/'
     subtype:  subclass_of_or_equal (set_or_class,set_or_class)
        subtype:  subclass__subclass_of (set_or_class,set_or_class)  if the common reading conventions of parameters had been respected, this type would have been named subclass_of; every instance of the 1st argument is also an instance of the 2nd argument; a class may have multiple superclasses and subclasses
           subtype:  immediate_subclass__immediate_subclass_of (set_or_class,set_or_class)  the 1st argument is a subclass of the 2nd argument and there is no other subclass of the 2nd argument such that the 1st is also a subclass of the 2nd; in WebKB, use the link '<'
        subtype:  sub_class_of__subclassof__super_class__superclas (class,class)  in WebKB, use the link '<'
     subtype:  power_set_fn__powersetfn (set_or_class -> set_or_class)  maps the argument to the set_or_class of all its subclasses
     subtype:  relation_to_another_class (class,class+)
        subtype:  sub_class_of__subclassof__super_class__superclas (class,class)  in WebKB, use the link '<'
        subtype:  equivalent_class (class,class)  in WebKB, use the link '='
        subtype:  exclusive_class__exclusiveclas (class,class)  the 2 classes have no common subtype/instance; in WebKB, use the link '!'
        subtype:  restricted_by (class,restriction)
        subtype:  disjoint_decomposition (class,class+)  a disjoint_decomposition of a class C is a set of mutually disjoint subclasses of C
           subtype:  partition (class,class+)  a partition of a class C is a set of mutually disjoint classes (a subclass partition) covering C; each instance of C is instance of exactly one of the subclasses in the partition
        subtype:  exhaustive_decomposition (class,class+)  an exhaustive_decomposition of a class C is a set of subclasses of C such that every instance of C is an instance of one of the subclasses in the set; note:  this does not necessarily mean that the elements of the set are disjoint (see sumo#partition - a partition is a disjoint exhaustive decomposition)
           subtype:  partition (class,class+)  a partition of a class C is a set of mutually disjoint classes (a subclass partition) covering C; each instance of C is instance of exactly one of the subclasses in the partition