Lesson 2: 1, 2
Exercise 2: 1

Lesson 3: 1, 2, 3, 4, 5
Exercise 3: 1, 2

Lesson 4: 1
Exercise 4: 1, 2, 3, 4

Lesson 5: n/a
Exercise 5: 1

Lesson 6: n/a
Exercise 6: not done yet