Timeline for What are your favorite instructional counterexamples?
Current License: CC BY-SA 4.0
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| Dec 19, 2022 at 15:43 | history | edited | Martin Sleziak | CC BY-SA 4.0 |
http -> https (the question was bumped anyway)
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| Mar 3, 2010 at 14:05 | comment | added | Joseph Malkevitch | Part of why Desargues "Theorem" is intriguing is that it holds in some projective planes and not in others. There are finite planes where it holds and finite planes where it does not hold. If there is a way to introduce coordinates for the plane with numbers from a division ring then then Desargues Theorem will hold. It also holds for projective planes sitting in higher dimensional projective spaces. In the real projective plane the theorem holds. The Moulton plane is a fascinating example. | |
| Mar 2, 2010 at 10:33 | history | answered | John Stillwell | CC BY-SA 2.5 |