Alternation for sublogarithmic space-bounded alternating pushdown automata

Jianliang Xu, Tsunehiro Yoshinaga, Katsushi Inoue, Yue Wang, Akira Ito
2001 Theoretical Computer Science  
This paper investigates inÿnite hierarchies on alternation-depth and alternation-size of alternating pushdown automata (apda's) with sublogarithmic space. We ÿrst show that there is an inÿnite hierarchy on alternation-depth for apda's with sublogarithmic space. We next investigate a relationship between alternation-depth and alternation-size, and show that for sublogarithmic space-bounded apda's, alternation-depth k is better than alternation-size k for each k¿3. We ÿnally show that there is an
more » ... inÿnite hierarchy on alternation-size for apda's with sublogarithmic space.
doi:10.1016/s0304-3975(00)00035-9 fatcat:4izv42dohncdviygyaqwnwaay4