Yuri Leonidovich Ershov Klaus Keimel Ulrich Kohlenbach Andrei Morozov Preface. 249-250 2009 159 Ann. Pure Appl. Logic 3 http://dx.doi.org/10.1016/j.apal.2008.10.002 db/journals/apal/apal159.html#ErshovKKM09