The work that this book represents is something I have wanted to do since 1979. While in Ireland, probably in 2001, I sketched some parts of a small operating system speci?cation in Z but left it because of other duties. In 2002, I worked on the sketches again but was interrupted. Finally, in April, 2005, I decided to devote some time to it and produced what amounted to a ?rst version of the kernel to be found in Chapter 3 of this book. I even produced...