Centro-Affine Geometry

The branch of affine geometry in which one studies invariants of centro-affine transformations: $ \overline{x}\; {} ^ {i} = A _ {s} ^ {i} x ^ {s} $. Centro-affine transformations leave one point (the centre) fixed. In centro-affine geometry there is complete duality: To every proposition concerning points corresponds the same proposition concerning hyperplanes.