One of the first formal proof systems. This is actually understandable!

TODO what are its limitations? Why were other systems created?

- Formal system | 0, 39, 2
- Formal proof | 15, 144, 8
- Formalization of Mathematics | 439, 818, 20
- Mathematics | 17, 10k, 239
- Ciro Santilli's Homepage | 238, 147k, 2k

- Busy beaver | 255
- Formalization of Mathematics | 439, 818, 20
- Metamath | 14
- Website front-end for a mathematical formal proof system | 718