4. 12.9, page 127.
5. 12.13, page 128.
6. 12.14, page 128.
7. Prove the following: if y-x>n for
a natural number n, then there exist n distinct
integers in the interval (x, y).
8. Prove the following: if y-x is at least 1,
then there exists an integer n in the interval [x, y].
Please do the part of the homework below which corresponds to
the topics covered in the lectures.