Atsuyuki Inoue Akira Ito Katsushi Inoue Tokio Okazaki Some properties of one-pebble Turing machines with sublogarithmic space. 138-149 2005 341 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2005.04.003 db/journals/tcs/tcs341.html#InoueIIO05