haven't; hasn't; doesn't exist; to not have; to not be[cedict]
钻牛角尖
zuān niú jiǎo jiānㄗㄨㄢ ㄋㄧㄡˊ ㄐㄧㄠˇ ㄐㄧㄢ
lit. to hone a bull's horn (成语 saw); fig. to waste time on an insoluble or insignificant problem; to bash one's head against a brick wall; a wild goose chase; a blind alley; to split hairs[cedict]