| ▲ | BigTTYGothGF 2 hours ago | |
> if you exclude the parallel postulate but use all of the other axioms from Euclid you get hyperbolic geometry No, you don't. (You need to replace the parallel postulate with a different one) | ||
| ▲ | seanhunter an hour ago | parent [-] | |
Thank you for the correction I actually didn't realise that so have learned something. Specifically for people who are interested it seems you have to replace the parallel postulate with a postulate that says every point is a saddle point (which is like the centre point of a pringle if you know what that looks like). | ||