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Zadrozny on Cardinalities and Well-Orderings

Zadrozny does not believe in a ``super theory'' of commonsense reasoning about sets, but rather in commonsense theories involving different aspects of sets. He thinks that these can be separately modeled in an existing set theory. In particular, he proposed a representation scheme based on Barwise's KPU for cardinality functions, hence distinguishing reasoning about well-orderings from reasoning about cardinalities and avoiding the box problem mentioned earlier (Zadrozny 1989).

Zadrozny interprets sets as directed graphs and does not assume the FA. A graph in his conception is a triple where V is a set of vertices, SE is a set of edges, and E is a function from a subset of SE into . It is assumed that if and only if there exists an edge between x and y. He defines the edges corresponding to the members of a set as

In classical set theory, the cardinality of a finite set s is a one-to-one function from a natural number n onto a set, i.e., a function from a number onto the nodes of the graph of the set. However, Zadrozny defines the cardinality function as a one-to-one order preserving mapping from the edges of a set s into the numerals Nums (an entity of numerals which is linked with sets by existence of a counting routine denoted by #, and which can take values like 1,2,3,4, or 1,2,3, about-five, or 1,2,3, many). The last element of the range of the function is the cardinality. The representation of the four element set with three atoms and one two-atom set is shown in Figure 17. The cardinality of the set is about-five, i.e., the last element of Nums which is the range of the mapping function from the edges of the set. (The cardinality might well be 4 if Nums was defined as 1,2,3,4.) Zadrozny then proves two important theorems in which he shows that there exists a set x with n elements which does not have a well ordering and there exists a well ordering of type n, i.e., with n elements, the elements of which do not form a set.

More recent work of Zadrozny treating different aspects of computational mereology vis--vis set theory can be found in (Zadrozny & Kim 1993).

  
Figure 17: The one-to-one order preserving cardinality function of Zadrozny (adapted from (Zadrozny 1989))



next up previous
Next: Protosets of Mislove Up: Some Interesting Attempts Previous: Perlis's Commonsense Set



Varol Akman
Sat Jan 13 15:54:04 EET 1996