Quadratic set

In mathematics, a quadratic set is a set of points in a projective plane/space which bears the same essential incidence properties as a quadric (conic section in a projective plane, sphere or cone or hyperboloid in a projective space).

Let ${\displaystyle {\mathfrak {P}}=({\mathcal {P}},{\mathcal {G}},\in )}$ be a projective space. A quadratic set is a non-empty subset ${\displaystyle {\mathcal {Q}}}$ of ${\displaystyle {\mathcal {P}}}$ for which the following two conditions hold:

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