Exercise 4.1 https://bit.ly/2KHknRg
Exercise4.2 https://bit.ly/2MqqwTV
Exercise4.3 https://bit.ly/31TSpYj
Exercise4.4 https://bit.ly/2TLkcqQ
Exercise4.5 https://bit.ly/31S20yJ
Exercise4.6 https://bit.ly/2TMBnYY
Examples https://bit.ly/31I5GmC