Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

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Bessel & Legendre Domain Survival

Pick which pair of Bessel functions is actually orthogonal, or match a domain's own symmetry to Bessel vs. Legendre -- one mixed-up special function ends the round.

💀 3 lifeives 🚫 no clock

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