  Several incidence theorems of planar projective geometry are considered. It
is demonstrated that generalizations of Pascal theorem due to M\"obius give
rise to double cross-ratio equation and Hietarinta equation. The construction
corresponding to the double cross-ratio equation is a reduction to a conic
section of some planar configuration $(20_3 15_4)$. This configuration provides
a correct definition of the multidimensional quadrilateral lattices on the
plane.
