Hannah Cairo was stuck on a math problem. All she could think about during those weeks was a new approach. “After months of trying to prove the result, I managed to understand why it was so difficult. I realized that if I used that information correctly, I might be able to refute the claim. Finally, after several failed attempts, I found a way to construct a counterexample [a case that does not satisfy the studied property and therefore proves it is not universally true].” Ciaro says it required...