Relation pm#relation_from_type_to_collection (type,collection)
  supertype:  relation_between_collections  relation_from_type
  subtype:  partition (type,collection)
  subtype:  instances__instance (type -> collection)
  subtype:  subtypes (type -> collection)
  subtype:  relation_from_class_to_collection (class,collection)
     subtype:  union_of__unionof (class,list)  for unionOf(X,L) read: X is the union of the classes in the list L; i.e. if something is in any of the classes in L, it is in X, and vice versa
        subtype:  disjoint_union_of (class,list)  for disjointUnionOf(X,L) read: X is the disjoint union of the classes in the list L: (a) for any c1 and c2 in L, disjointWith(c1,c2), and (b) i.e. if something is in any of the classes in L, it is in X, and vice versa
     subtype:  intersection_of (class,list)  for intersectionOf(X,Y) read: X is the intersection of the classes in the list Y; i.e. if something is in all the classes in Y, then it's in X, and vice versa
     subtype:  one_of__oneof (class,list)  for oneOf(C,L) read everything in C is one of the things in L
     subtype:  distinct_members (all_different,list)
     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:  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:  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