Getting to know problems

I recently had a student writing to me asking for advice on problem-solving. The student gave a few examples of problems they didn&rsquo;t solve (like I tell people to ). One of the things that struck me about the message was their description of their work on USAMO 2021/4 , whose statement reads: A finite set S S S of positive integers has the property that, for each s ∈ S s\in S s ∈ S , and each…