The Dual Theorem of Pappus

In P², given lines a, b, c passing through a point L, and lines a', b', c' passing through a point L', let P be the line through the points (a ¡û b') and (a' ¡û b). Similarly let Q be the line through the poins (a ¡û c') and (a' ¡û c), and R be the line through the poins (b ¡û c') and (b' ¡û c). Then lines P, Q, R are coincident.