[Freudenthal's magic square][1] of Lie algebras<br> and the corresponding square of projective planes: ℝP<sup>2</sup> ℂP<sup>2</sup> ℍP<sup>2</sup> ↀP<sup>2</sup> ℂP<sup>2</sup> (ℂ⊗ℂ)P<sup>2</sup> (ℂ⊗ℍ)P<sup>2</sup> (ℂ⊗ↀ)P<sup>2</sup> ℍP<sup>2</sup> (ℍ⊗ℂ)P<sup>2</sup> (ℍ⊗ℍ)P<sup>2</sup>$ (ℍ⊗ↀ)P<sup>2</sup> ↀP<sup>2</sup> (ↀ⊗ℂ)P<sup>2</sup> (ↀ⊗ℍ)P<sup>2</sup> (ↀ⊗ↀ)P<sup>2</sup> <i>Also:</i> have a look at [John Baez's cheat sheet][2],<br> and at the subsections <i>[G][3]</i><sub>2</sub>, <i>[F][4]</i><sub>4</sub>, <i>[E][5]</i><sub>6</sub>, <i>[E][6]</i><sub>7</sub>, <i>[E][7]</i><sub>8</sub>. [1]: http://en.wikipedia.org/wiki/Freudenthal_magic_square [2]: http://math.ucr.edu/home/baez/octonions/node13.html [3]: http://math.ucr.edu/home/baez/octonions/node14.html [4]: http://math.ucr.edu/home/baez/octonions/node15.html [5]: http://math.ucr.edu/home/baez/octonions/node17.html [6]: http://math.ucr.edu/home/baez/octonions/node18.html [7]: http://math.ucr.edu/home/baez/octonions/node19.html