text: a = [1,2,3]
  b = [2,3,4,5,6]
  c = []
  
  for aa in a:
      found = True
      for bb in b:
          if (aa == bb):
              found = False
              break
      if (found):
          c.append(aa)
  
  
  for aa in b:
      found = True
      for bb in a:
          if (aa == bb):
              found = False
              break
      if (found):
          c.append(aa)
  
  print(c)
  
  
  # shortcut
  print(set(a) ^ set(b))