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| | Algebraic surfaces |
 | | A Tritangent of a cubic surface is a plane which intersects the cubic surface in the union of three lines (instead of a irreducible cubic curve), and the three intersection points of the three lines are then tangent points, hence the name. |
 | | There are several special kinds of quartic surfaces, the Kummer surfaces, named after W. Kummer, the symmetroids, which are the zero locus of the determinant of a symmetric 4 x 4 matrix of linear forms, and the desmic surfaces, so-called because of their relation to desmic tetrahedra. |
 | | As far as the desmic surfaces are concenrned, these are more special than the symmetroids: there is just a one-dimensional family of them, and they have 12 ordinary double points, which are the vertices of three tetrahedra in three-space. |
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