What we have feared during the last weeks and months came true yesterday
morning: Clemens
Lautemann died at the age of 53 from cancer.
Most recently Lautemann had been working on logical characterizations
of complexity classes but I will remember him most for his beautiful
proof (or here)
that BPP, the class of languages with efficient
probabilistical computatins, is in the second level of the polynomial-time
hierarchy. In 1983 Sipser had shown BPP in the fourth level, and very
soon after Gács and Lautemann independently showed BPP in the second
level. Lautemann gave a very simple combinatorial
proof that I consider one of the prettiest applications of the
probabilistic method to complexity.