Relation pm#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
  supertype:  relation_between_collections  relation_to_set_or_class
  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