We report results from large-scale experiments in satissability testing. As has been observed by others, testing the satissability of random formulas often appears surprisingly easy. Here we show that by using the right distribution of instances, and appropriate parameter values, it is possible to generate random formulas that are hard, that is, for which satissability testing is quite diicult....

Aweak completeness phenomenon is investigated in the complexity class E = DTIME(2linear). According to standard terminology, a language H is m-hard for E if the set Pm(H), consisting of all languages A m H , contains the entire class E. A language C is P m-complete for E if it is m-hard for E and is also an element of E. Generalizing this, a language H is weakly m-hard for E if the set Pm(H) do...

We report results from large-scale experiments in satisfiability testing. As has been observed by others, testing the satisfiability of random formulas often appears surprisingly easy. Here we show that by using the right distribution of instances, and appropriate parameter values, it is possible to generate random formulas that are hard, that is, for which satisfiability testing is quite diffi...

Coreference resolution is a key problem in natural language understanding that still escapes reliable solutions. One fundamental difficulty has been that of resolving instances involving pronouns since they often require deep language understanding and use of background knowledge. In this paper we propose an algorithmic solution that involves a new representation for the knowledge required to a...