input: Write a function to find the maximum element in a list using recursion.
  assert find_maximum([3, 9, 7, 6]) == 9
  assert find_maximum([1, 2, 3, 4, 5]) == 5
  assert find_maximum([10, 9, 8, 7, 6, 5]) == 10
output: def find_maximum(lst):
      if len(lst) == 1:
          return lst[0]
      else:
          max_of_rest = find_maximum(lst[1:])
          return lst[0] if lst[0] > max_of_rest else max_of_rest