topic: 8.9
exercise: 8.9
topic: 8.10
exercise: 8.10
topic: 8.11
exercise: 8.11
topic: 8.12
exercise: 8.12
topic: 8.13
exercise: 8.13
topic: 8.14
exercise: 8.14
topic: 8.15
exercise: 8.15
topic: 8.16
exercise: 8.16
topic: 8.17
exercise: 8.17
topic: 8.18
exercise: 8.18