Set-Builder Form: Describing elements using a property
Example: A = {x | x ∈ N and x < 4}

1. A well-defined collection is called a ______.
2. The symbol for empty set is ______.
3. The set of natural numbers less than 1 is ______.
4. A set with one element is called a ______ set.
5. The number of elements in a set is called its ______.
6. The set {1,2,3} is ______.
7. The set of natural numbers is ______.
8. The set {x | x ∈ N, x < 4} is equal to ______.
9. The cardinal number of ∅ is ______.
10. The set of vowels has ______ elements.
11. Order of elements in a set is ______.
12. Repetition of elements in a set is ______.
13. The set {1,1,2} is equal to ______.
14. Which is not a set: collection of good students / months in a year?
15. The set {x | x² = 4, x ∈ N} is ______.
16. ∅ is a ______ set.
17. The set {0} has ______ element(s).
18. The set of integers is ______.
19. n({a,e,i,o,u}) = ______.
20. A set must be ______ defined.