Schaefer proved in 1978 that the Boolean constraint satisfaction problem for a given constraint language is either in P or is NP-complete, and identified all tractable cases. Schaefer's dichotomy theorem actually shows that there are at most two constraint satisfaction problems, up to polynomial-time isomorphism (and these isomorphism types are ... more >>>

We show how to extract random bits from two or more independent
weak random sources, in cases where only one source is of linear
min-entropy and all other sources are of logarithmic min-entropy.
We also give improved constructions of mergers and condensers.
In all that comes below, $\delta$ is an ... more >>>

We show that for any constant a, ZPP/b(n) strictly contains
ZPTIME(n^a)/b(n) for some b(n) = O(log n log log n). Our techniques
are very general and give the same hierarchy for all the common
promise time classes including RTIME, NTIME \cap coNTIME, UTIME,
MATIME, AMTIME and BQTIME.

We show a ... more >>>