(x

i.e. preservation of the cross ratio of the four points, which means explicitly:

The fixed points of the homography (the coordinates) satisfy the equation:

Single out two of the 5 points A, B and join them with the other three {C,D,E}.

By the aforementioned theorem the intersection points of the pencil {AC,AD,AE} and the pencil {BC,BD,BE} with the line L define three points {x

The intersection points M, N of the line L with the conic are the fixed points of this homography on L.

Carying out the operations in terms of {x

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