Mathematical Conversations
Open Books and Secret Agents
An open book is a topological concept aptly named by Elmar Winkelnkemper.
The binding of the book is a fibred knot (of any dimension), and open books and fibred knots are essentially synonymous. Currently the standard reference for the existence and topology of these structures is a book by Andrew Ranicki, which, when opened, reveals an appendix by Winkelnkemper. Both of them are no longer alive, but they seem to have been quite friendly during their lifetime.
This is remarkable given their personal history: W’s father was an infamous Nazi, said to have been a US agent, and R’s father was an über-famous survivor of the Warsaw ghetto who was an agent for Polish intelligence after the war, before he was purged for ideological deviation. Mathematics certainly bridges differences!