Skip to main content
5 events
when toggle format what by license comment
Aug 30, 2018 at 15:25 vote accept Kostya_I
Apr 29, 2016 at 16:24 comment added Kostya_I If you put the question as "whether the Desargues theorem is valid in any projective space as defined axiomatically", then, of course, I agree. But, I believe, this view has little to do with how Desargues seen his result - he just proved the theorem for "the plane" that is obviously embeddable to "space".
Apr 29, 2016 at 13:50 comment added Francesco Polizzi "but here the 3D result does readily imply the 2D one" Yes, but only for some projective planes, namely the ones where you can perform this lifting construction to the $3$-space. In fact, Desargues theorem is valid in all projective spaces of dimension $\geq 3$, but there are some non-desarguesian projective planes. So the case of dimension $2$ is really the tricky part here. Is not this precisely an example of what you are looking for?
Apr 29, 2016 at 12:43 comment added Kostya_I a nice answer, but here the 3D result does readily imply the 2D one (and, I believe, wasn't published earlier, am I right?), so it is not quite what I meant.
Apr 29, 2016 at 11:49 history answered Alexandre Eremenko CC BY-SA 3.0