Papadopoulos, Athanase (2014). "Hilbert's fourth problem". In Papadopoulos, Athanase; Troyanov, Marc (eds.). Handbook of Hilbert geometry. IRMA Lectures in Mathematics and Theoretical Physics. Vol. 22. European Mathematical Society. pp. 391–431. doi:10.4171/147-1/15. ISBN978-3-03719-147-7.
Papadopoulos, Athanase (2014). "Hilbert's fourth problem". In Papadopoulos, Athanase; Troyanov, Marc (eds.). Handbook of Hilbert geometry. IRMA Lectures in Mathematics and Theoretical Physics. Vol. 22. European Mathematical Society. pp. 391–431. doi:10.4171/147-1/15. ISBN978-3-03719-147-7.