Douglas Bridges is Professor Emeritus of Pure Mathematics at University of Canterbury, Christchurch, New Zealand. He is co-author, with the late Errett Bishop, of the monograph Constructive Analysis, as well as seven other books and almost 200 research papers in constructive mathematics. Hajime Ishihara is Professor of Mathematical Logic at Japan Advanced Institute of Science and Technology (JAIST). He has worked for over thirty years in constructive mathematics and mathematical logic, in which he is known for introducing 'Ishihara's tricks' and for opening up constructive reverse mathematics. Michael Rathjen was Professor of Mathematics at the Ohio State University and is currently Professor of Mathematics at the University of Leeds, England. His main research area is mathematical logic, especially proof theory, ordinal analysis, constructive and alternative set theories as well as intuitionism. Helmut Schwichtenberg is Professor Emeritus of Mathematics at Ludwig-Maximilians-Universität, Munich, Germany. He is co-author of the monographs Basic Proof Theory (1996, 2000) and Proofs and Computations (2012).