Takeshi Koshiba Erkki Mäkinen Yuji Takada Inferring pure context-free languages from positive data. 469-477 2000 14 Acta Cybern. 3 http://www.inf.u-szeged.hu/kutatas/actacybernetica/vol14n3/cikk4.xml db/journals/actaC/actaC14.html#KoshibaMT00