Chapter 2 - Set Theory - Chapter Summary, Review, and Test - Review Exercises - Page 109: 20

Ø ⊆ {X | X is an odd natural number}

Ø {X | X is an odd natural number} The first set is Ø which represents the empty set, and we know that empty set is the subset of every set. So first set is the subset of the second set. Ø ⊆ {X | X is an odd natural number}