Description: This book describes a formalism to describe simultaneously and side by side classical and quantum physical systems. It is mathematically completely equivalent to the standard description, but it makes it more easy to compare the two type of systems. It is attractive because it unifies different systems, but it has also interesting applications, some of which are discussed in this book.There is a very important application, namely to the interpretation of quantum theory, a subject on which an enormous literature exists. With this formalism it can be rigorously shown that most of this literature is erroneous, or irrelevant, at best. This will be treated in a future publication. Peter Bongaarts taught for 35 years theoretical and mathematical physics at the University of Leiden. In 2015 he published "Quantum Theory. A Mathematical Approach".
