Using Abstrips abstractions - Where do we stand?

Many experimental and theoretical results have been provided which analyze the effects of Abstrips abstractions in search problems. Some of these resu lts are positive, i.e. show gains in efficiency; some are negative and seem to contradict, at least partially, the positive results. The aim of this n ote is to provide an analysis of how Abstrips abstractions work, and use it to provide an explanation of the main results which can be found in the li terature.