Krzysztof R. Apt is a Fellow at CWI (Centre Mathematics and Computer Science) in Amsterdam and Affiliated Professor at the University of Warsaw. He is also Professor Emeritus at the University of Amsterdam. He earned his Ph.D. degree in mathematics from the Polish Academy of Sciences in Warsaw in 1974. During his scientific career, he held tenure positions in Poland, France, the USA, and the Netherlands. Apt published four books and several articles in computer science, mathematical logic, and, more recently, theoretical economics. In computer science his research interests have included program correctness and semantics, use of logic as a programming language, design of programming languages, distributed computing, and algorithmic game theory. For the past 20 years he has been involved in a number of initiatives aiming at open access to scientific publications. He is a member of Academia Europaea, the founder and first Editor-in-Chief of the ACM Transactions on Computational Logic, and past president of the Association for Logic Programming. Together with Tony Hoare, he is the editor of this volume.

Tony Hoare was on the faculty of the Queen's University of Belfast from 1968 until 1977. He moved to Oxford University as Professor of Computation in 1977, where he remained until his retirement from academia in 1999. Shortly thereafter he joined the Microsoft Research Laboratory in Cambridge (UK). His research has spanned several aspects of programming including design of data structures and programming languages, program verification, and concurrency. He invented Quicksort, conceived Hoare logic, proposed (jointly with Per Brinch Hansen) the concept of a monitor, and introduced Communicating Sequential Processes both as a language for distributed programming and, later, as a formalism to reason about concurrency and nondeterminism. His more recent work is concerned with the Unifying Theories of Programming. Hoare received the Turing Award in 1980, the Harry H. Goode Memorial Award in 1981, the Kyoto Prize in 2000, and the IEEE John von Neumann Medal in 2011. In 2000, he was knighted by the British Queen for services to education and computer science. He holds honorary doctorates from several universities and is a fellow or foreign member of various learned societies, including the UK Royal Society, the UK Royal Academy of Engineering, the US National Academy of Sciences, the US National Academy of Engineering, and the Computer History Museum. Together with Krzysztof R. Apt, he is the editor of this volume.