A Question
I was reading through Tibor Karolyi's Alexander Beliavsky - Legendary Chess Careers - Part 1 (recommended!), and learned (on p. 111) that Beliavsky is tied with Paul Keres and Viktor Korchnoi for having defeated nine different world champions during their careers. (If Fabiano Caruana becomes world champion someday, then Korchnoi and Beliavsky will still be tied, but at 10, but if Nakamura earns the title Beliavsky will be in clear first.)
But what I'd like to know is this: what player has defeated the most world champions during their championship reigns? Let's make it a two-parter: which world champion has the most such scalps, and which non-world champ does? In addition to the world champions, Keres, and Korchnoi, I'd also start by checking on Bronstein and Geller.