Exer. 8.1
Exer. 8.2
Exer. 8.3
Exer. 8.4
Exer. 8.4, another solution
Exer. 8.5
Exer. 8.5, fixed (?) answer
Exer. 8.6
Exer. 8.7
Exer. 8.7: about Penrose's intentions, and a solution.
Exer. 8.7 another solution
Exer. 8.8