old_contents: def is_leap_year(y):
      if y % 400 == 0:
          return True
      elif y % 100 == 0:
          return False
      elif y % 4 == 0:
          return True
      else:
          return False
  
new_contents: def is_leap_year(y):
      return (y % 4 == 0) and (y % 100 != 0 or y % 400 == 0)
  
subject: Combine tests into one