F = { { Ø }, (x + y), 1/4, 1/3, 1/2, A, B, C, D } Yes, the 9 elements of F are 1. { Ø } 2. (x + y) 3. 1/4 4. 1/3 5. 1/2 6. A 7. B 8. C 9. D So you are right, the cardinality (count) is 9. Comment: The set { Ø } is not empty because it contains one element, the empty set Ø. And Ø is only an element of { Ø } and not an element of F. The element (x + y) is a single number depending upon what number x and y are. Edwin