Complexity Theory Column 48

Here is a real gift to the field from David Johnson: After a thirteen year intermission, David is restarting his NP-completeness column. His column will now appear about twice yearly in ACM Transactions on Algorithms. Welcome back David, and thanks! And for those for whom a diet of two per year won’t do, meals past can be found at http://www.research.att.com/ ̃dsj/columns.html. As to the Complexity Theory Column, warmest thanks to Elvira, Jack, and John for their wonderful guest column on The Fractal Geometry of Complexity Classes in this issue. Upcoming articles include Neil Immerman on Recent Progress in Descriptive Complexity, Piotr Faliszewski and me on Open Questions in the Theory of Semifeasible Computation, and Omer Reingold on a topic TBA.