Today’s combinatorics seminar at Alfréd Rényi was by Christian Reiher, the second-most successful International Math Olympiad competitor so far, and still the top when I was the alternate in 2007. (He was recently overtaken by Lisa Sauermann, which is impressive enough itself that it seems superfluous to point out that she also broke several records for girls’ IMO performance.)

Also, as an example of that even the best mathematicians make mistakes, he flipped an inequality, realized something was wrong, and caught blackboard blindness, and I found and pointed it out first. 🙂