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