Infinity symbol in bookbinding to indicate that a book is printed on acid-free paper and will therefore be long-lasting. In modern mysticism, the infinity symbol has become identified with a variation of the ouroboros, an ancient image of a snake eating its own tail that has also come to symbolize the infinite, and the ouroboros is sometimes drawn in figure-eight form to reflect this identification, rather than in its more traditional circular form. In the works of Vladimir Nabokov, including "The Gift" and "Pale Fire", the figure-eight shape is used symbolically to refer to the Möbius strip and the infinite, for instance
Plane at infinity does make it look "special" in comparison to the other planes of the space. If the affine 3-space is real, formula_2, then the addition of a real projective plane formula_3 at infinity produces the real projective 3-space formula_4. Since any two projective planes in a projective 3-space are equivalent, we can choose a homogeneous coordinate system so that any point on the plane at infinity is represented as ("X":"Y":"Z":0). Any point in the affine 3-space will then be represented as ("X":"Y":"Z":1). The points on the plane at infinity seem to have three degrees of freedom, but homogeneous coordinates are equivalent