HoF: map defined using list comprehensions
HoF: map defined using recursion
HoF: filter defined using list comprehensions
HoF: filter defined using recursion
HoF: sumSqrEven (example of map and filter working together)
HoF: all defined using recursion
HoF: any defined using recursion
HoF: takeWhile defined using recursion
HoF: dropWhile defined using recursion
HoF: foldr defined using recursion
HoF: sum defined using foldr
HoF: product defined using foldr
HoF: or defined using foldr
HoF: and defined using foldr