import sys cu = ['Niuniu', 'Niumei', 'GURR', 'LOLO'] cu_l = [j.lower() for j in cu] nu = ['GurR', 'Niu Ke Le', 'LoLo', 'Tuo Rui Chi'] for i in nu: if i.lower() in cu_l: print('The user name {} has already been registered! Please change it and try again!'.format(i)) else: pri...