How large can a subset be???
11:27
One from Hong Kong.
10:16
Linear Second Order Homogeneous Differential Equations with Constant Coeff - (2 distinct real roots)
5:27
Radius of Convergence: The Exponential Function
26:23
Two from Thailand!
20:08
A number theory problem from Morocco!
26:06
The 60 Year Quest for the Perfect Sofa
14:33
a RARE mistake from Euler (AIME 1989)
35:21