Burchard von Braunmühl Romain Gengler Robert Rettinger The Alternation Hierarchy for Machines with Sublogarithmic Space is Infinite. 85-96 1994 conf/stacs/1994 STACS db/conf/stacs/stacs94.html#BraunmuhlGR94 http://dx.doi.org/10.1007/3-540-57785-8_133