1. Arzarello, F., Micheletti, C., Olivero, F., Robutti, O., and Paola, D. (1998): A model for analysing the transition to formal proofs in geometry.—In: A. Olivier & K. Newstead (Eds.),Proceedings PME 22 (v. 2). Stellenbosch, South Africa, pp. 24~31.
2. Bachelard, G. (1938):La formation de l’esprit scientifique.— Paris: Vrin.
3. Balacheff, N. (1999): Contract and custom: Two registers of didactical interactions.—In:The Mathematics Educator, 9, 23~29.
4. Brousseau, G. (1997),Theory of didactical situations in mathematics: Didactique des Mathematiques 1970~1990 (N. Balacheff, M. Cooper, R. Sutherland, and V. Warfield, Eds. and Trans.).—Dordrecht, The Netherlands. Kluwer.
5. Chauvenet, W. (1898):Treatise on elementary geometry (Revised and abridged by W. Byerly). Cambridge, MA: Lippincott. (Original revision published in 1887)