My deepest thanks go to my mathematics teacher, Dr. Franz Hagen, who guided and supported me from the 9th grade through to my Abitur at Gymnasium Oer-Erkenschwick. He was the one who awakened my joy in mathematics and recognized what may have been a talent. I dedicate this website to him.

I am also grateful to the many colleagues around the world who kindly took the time to answer my questions, offer constructive criticism of my texts and ideas, or support me in other ways. In addition, I would like to mention the following people in alphabetical order.