ex8.rb

derivative_of_square = nth_derivator.(1).(square) #derivate one time
second_derivative_of_square = nth_derivator.(2).(square) #derivate two times
third_derivative_of_square = nth_derivator.(3).(square) #derivate three times
p derivative_of_square.(3) # => 5.999999999999339
p second_derivative_of_square.(3) # => 2.000000000279556
p third_derivative_of_square.(3) # => 0.0