Simultaneity is harder than agreement

Is Belief Revision Harder Than You Thought?

Suppose one wishes to construct, use, and maintain a knowledge base (KB) of beliefs about the real world, even though the facts about that world are only partially known. In the AI domain, this problem arises when an agent has a base set of beliefs that reflect partial knowledge about the world, and then tries to incorporate new, possibly contradictory knowledge into this set of beliefs. We cho...

Static Equivalence is Harder than Knowledge

There are two main ways of defining secrecy of cryptographic protocols. The first version checks if the adversary can learn the value of a secret parameter. In the second version, one checks if the adversary can notice any difference between protocol runs with different values of the secret parameter. We give a new proof that when considering more complex equational theories than partially inve...

Uniform consensus is harder than consensus

We compare the consensus and uniform consensus problems in synchronous systems. In contrast to consensus, uniform consensus is not solvable with byzantine failures. This still holds for the omission failure model if a majority of processes may be faulty. For the crash failure model, both consensus and uniform consensus are solvable, no matter how many processes are faulty. In this failure model...

Why Is Simulation Harder than Bisimulation?

Why is deciding simulation preorder (and simulation equivalence) computationally harder than deciding bisimulation equivalence on almost all known classes of processes? We try to answer this question by describing two general methods that can be used to construct direct one-to-one polynomial-time reductions from bisimulation equivalence to simulation preorder (and simulation equivalence). These...

Data Integration Is Harder than You Thought