In section 3.1 we insisted that a polygon should have no three successive vertices collinear. However, other collinearities are allowed. In particular, theorem 3.51 (pappus's theorem) may be rephrased as follows:
In section 3.1 we insisted that a polygon should have no three successive vertices collinear.However, other collinearities are allowed. In particular, theorem 3.51 (pappus's theorem) may be rephrased as follows: