exercise 29: simpson 's rule for calculating integrals
now use the 'sum' hof for simpson-integral
exercise 30 : iterative version if sum hof
exercise 31: product
exercise 32: accumulate function to abstract sum and product. iterative and recursive process
exercise 33: filtered accumulate
exercise 35: compute the golden ratio through a fixed point function approximation
Exercise 36: fixed-point of x^x
Exercise 34