import sys c_users = ['Niuniu','Niumei','GURR','LOLO'] n_users = ['GurR','Niu Ke Le','LoLo','Tuo Rui Chi'] is_same = 0 for i in n_users: for j in c_users: if(i.upper() == j.upper()): print(f'The user name {i} has already been registered! Please change it and try again!') is_same = 1 break if(is_same...