Richard J. Lipton Mitsunori Ogihara Yechezkel Zalcstein A Note on Square Rooting of Time Functions of Turing Machines. 295-299 2003 36 Theory Comput. Syst. 3 http://dx.doi.org/10.1007/s00224-002-1079-x db/journals/mst/mst36.html#LiptonOZ03