Takashi Moriyama Masako Sato Properties of Language Classes with Finite Elasticity. 532-538 1995 78-D IEICE Trans. Inf. Syst. 5 http://search.ieice.org/bin/summary.php?id=e78-d_5_532 db/journals/ieicet/ieicet78d.html#MoriyamaS95