效绵 So far... some language {anbn|n≥0} decidable all languages regular languages context free languages RE {abcn|n≥0} We will show a natural undecidable L nextSo far… ◼ We will show a natural undecidable L next. regular languages context free languages all languages decidable RE {a nb n | n ≥ 0} {a nb nc n | n ≥ 0} some language