- If and , then C.
- The complementary set in of the set of all the even natural numbers is the set of all the odd natural numbers.

- (i)
- ;
- (ii)
- ;
- (iii)
- .

- (i)
- .
- (ii)
- This is a straightforward consequence of the definition of the complementary set.
- (iii)
- For any , the proposition is a contradiction.

- (i)
- ;
- (ii)
- .

- .