Open Problems

A number of questions have been raised and not answered in the course of this book. Foremost among these are issues concerning extensions of the reliabilities and informativeness of the search algorithms. We record here a number of other questions that seem important. Some of the problems and questions may be quite easy, or may follow from results already available but unknown to us. Others have been worked at for some time by ourselves or others and appear to be quite difficult. Some are not particularly difficult but require work we have not done. All of the issues seem to us important to help fill out our understanding of the relations between causal structure and probability, and of the possibilities of causal inference and prediction.