current_users=['Niuniu','Niumei','GURR','LOLO'] lowercurrent_users=[] new_users=['GurR','Niu Ke Le','LoLo','Tuo Rui Chi'] lowercurrent_users=list(map(str.lower,current_users)) for i in new_users: if i.lower() in lowercurrent_users: print(f'The user name {i} has already been registered! P...