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List of simple but counterintuitive math things
Insane trigonometric identities
Упражнения для сестры, часть 1
Упражнения для сестры, часть 2
Упражнения для сестры, часть 3
Упражнения для сестры, часть 4
Elliptic functions and their friends
Derivation of the Weierstrass elliptic integral periods
Pi and the AGM: Exercises 1.1
Pi and the AGM: Exercises 1.2
Useful German vocab for math writing
Russian case inflection cheatsheet