\begin{definition}[Definition:Dandelin Spheres/Parabola]
Let $\CC$ be a double napped right circular cone with apex $O$.
Let $\PP$ be a plane which intersects $\CC$ to form a parabola.
Then it is possible to construct one sphere $\SS$ so that it has ring-contact with $\CC$ such that $\PP$ is tangent to both $\SS$.
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\end{definition}