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Next: The Inclusion-Exclusion Principle Up: Relations and Functions Previous: Some Definitions

Some Counting Questions

When we write |X|=m, we mean that X is a finite set that contains exactly m elements; i.e., the cardinality of X is m.

  1. If |X|=m and |Y|=n, how many relations between X and Y are there?
  2. If |X|=m and |Y|=n, how many functions tex2html_wrap_inline253 are there?
  3. Suppose |X|=m, |Y|=n, and tex2html_wrap_inline253 is a function. Try to fill in the following table by giving a formula for the number of functions in each case:

    displaymath291

  4. How many ways are there of removing a regular tetrahedron from the table and replacing it in the same position, but not necessarily with the same sides facing the same directions as before?
  5. How many ways are there of removing a cube from the table and replacing it in the same position, but not necessarily with the same sides facing the same directions as before?



Carl Lee
Wed Sep 30 08:36:10 EDT 1998