Good parametrizations and the first proof of Theorem 1. Let
C ⊂ RP
2 be a non-degenerate conic, and ` ⊂ RP
2 be a line. For any point
x ∈ C consider the central projection πx : ` → C. This map is called in [2,
Section 16.2] a “good parametrization” for the following reason.