The Six Lines
The picture above shows the six lines which are contracted to points
when mapped to the plane under the birational map determined
by the trihedral pair indicated via the orange and pink planes (for some specific 3 ×3 matrix).
All other points of the surface are mapped one-to-one to the points in the plane distinct from the six special points.
File translated from
TEX
by
TTH,
version 4.08.
On 4 Jun 2017, 11:23.