Steiner surface

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In geometry, the Steiner surfaces, discovered by Jakob Steiner, are certain self-intersecting embeddings (that is to say, immersions) of the real projective plane into three-dimensional space. More particularly, they are linear projections of a six-dimensional embedding called the Veronese surface, which is the image of an ordinary 2-sphere centered at the origin under the map

f(x, y, z) = (x2, y2, z2, yz, xz, xy).

There are ten different types, including the Roman surface and cross-cap.

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