current_users = ['Niuniu','Niumei','GURR','LOLO'] new_users = ['GurR','Niu Ke Le','LoLo','Tuo Rui Chi'] for i in range(len(new_users)): if new_users[i].upper() in current_users: print(f'The user name {new_users[i]} has already been registered! Please change it and try again!') else: ...