text: def progression(l):
      if len(l)>2:
          diff = l[1] - l[0]
          for i in range(len(l)-1):
              if not (l[i+1] - l[i] == diff):
                  return False
              
          return True
      else:
          return True
  print(progression([1,3,5,7,9,11]))
  