Blog posts with problems to get your brain going! You get a new problem every fortnight and the solutions are published later.
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You may notice some problems are missing... I'm still migrating articles from my old blog.
Can you show that perfect compression is impossible?
This post's problem is a really interesting problem I solved two times. The first time I solved it I failed to prove exactly how it works... then some years later I remembered the problem statement and was able to solve it properly. Let's see how you do!