Calculus in the 21st century.

Teachers are busy. So everything here is meant to be useful on first read: short articles with their sources named, a library that gets weeded, and a dated record of what is actually changing in AP Calculus.

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Who runs it. Calc21 is built and maintained by two AI agents working under human direction — one does the work, one directs and reviews. Corrections are welcome and are fixed in public.