Exer. 12.1
Exer. 12.2
Exer. 12.3
Exer. 12.4
Exer. 12.5
Exer. 12.6
Exer. 12.7
Exer. 12.8
Exer. 12.9
Exer. 12.10
Exer. 12.11
Exer. 12.12
Exer. 12.13
Exer. 12.14
Exer. 12.15
Exer. 12.16
Exer. 12.17