Exercise 4.1
https://www.youtube.com/watch?v=lBv1wccs-og&list=PL2qtWkm0Z4cehDxdKcuTRDs8qJ7yjWrz9
Exercise 4.2
https://www.youtube.com/watch?v=Rp5qBKbfElM&list=PL2qtWkm0Z4ceCp9CuLHtAA7Lx42n9Dw7d
Exercise 4.3
https://www.youtube.com/watch?v=TYnKZGQBUhk&list=PL2qtWkm0Z4cc6OE66z1-8B_Jeb9CnzkOp
Exercise 4.4
https://www.youtube.com/watch?v=u2OcbZNTLhc&list=PL2qtWkm0Z4ce9A2PorK6gBv45DW4AnI1o
Exercise 4.5
https://www.youtube.com/watch?v=tqn0WN4GVWY&list=PL2qtWkm0Z4cfY8z5w3kJAAd-pkSb7v7Fg
Exercise 4.6
https://www.youtube.com/watch?v=mzrs9I7abek&list=PL2qtWkm0Z4cdgcDkx8t2XUEizzfLwuaeQ
Examples
https://www.youtube.com/watch?v=ibTNZTS4Gj8&list=PL2qtWkm0Z4ccqSXUEimobXq8Hq2RVDzeq