input: Write a function to identify the second smallest element in a list.
  assert find_second_smallest([1, 2, -8, -2, 0, -2])==-2
  assert find_second_smallest([1, 1, -0.5, 0, 2, -2, -2])==-0.5
  assert find_second_smallest([2,2])==None
output: def find_second_smallest(lst):
      if len(lst) < 2:
          return None
      first_min = second_min = float('inf')
      for num in lst:
          if num < first_min:
              second_min, first_min = first_min, num
          elif first_min < num < second_min:
              second_min = num
      return second_min if second_min < float('inf') else None