input: Write a python function to modify a list by squaring each element and subtracting 2.
  assert modify_list([3, 5, 7, 9]) == [7, 23, 47, 79]
  assert modify_list([1, 2, 3, 4]) == [-1, 2, 7, 14]
  assert modify_list([10, 20, 30]) == [98, 398, 898]
output: def modify_list(lst):
      return [x**2 - 2 for x in lst]