Parent Page (Chapter 2. Incidence)      Following Page (2.5. Harmonic Conjugacy)

H.S.M. Coxeter.
The Real Projective Plane.

Springer Science & Business Media, 1992.

Chapter 2. Incidence.

2.4. Quadrangle and quadrilateral. Pp. 17 —

See this text in Russian there.

Parent Page (Chapter 2. Incidence)      Following Page (2.5. Harmonic Conjugacy)