Kurt Godel was one of the most outstanding logicians of the twentieth century, famous for his work on the completeness of logic, the incompleteness of number theory, and the consistency of the axiom of choice and the continuum hypothesis. He is also noted for his work on constructivity, the decision problem and the foundations of computation theory, as well as for the strong individuality of his writings on the philosophy of mathematics. He is less well known for his discovery of unusual cosmological models for Einstein's equations, in theory, permitting time travel into the past. The book is the fourth part of a five volume set, which is the first to make available all of Godel's writings in one place. The collected Works of Kurt Godel is designed to be useful and accessible to a wide audience without sacrificing scientific or historical accuracy.