Some Incidence Theorems and Integrable Discrete Equations
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Several incidence theorems of planar projective geometry are considered. It is demonstrated that generalizations of the Pascal theorem due to Mobius give rise to the double cross-ratio equation and the Hietarinta equation. The construction corresponding to the double cross-ratio equation is a reduction to a conic section of some planar configuration (203154). This configuration provides a correct definition of the multi-dimensional quadrilateral lattices on the plane.