1. P. Alexandroff and P. Urysohn, Memoire sur les espaces topologiques compacts’ Verhandelingen der Koninklijke Nederlandsche Akademie van Wetenschappen, Afdeeling Natuurkunde, vol. XIV, no. 1, Amsterdam, 1929.
2. American Mathematical Society Colloquium Publications, Vol. 25;Birkhoff, Garrett,1948
3. New foundations of projective and affine geometry;Menger, Karl;Ann. of Math. (2),1936
4. P. Urysohn, Der Hilbertsche Raum als Urbild der metrischen Räume, Math. Ann. vol. 92 (1923) pp. 302-304.
5. A note on complementation in lattices;Wilcox, L. R.;Bull. Amer. Math. Soc.,1942