The following is a tentative list.
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Arcavi, A. (2003). The role of visual representations in the learning of mathematics. Educational Studies in Mathematics, 52(3), 215–241.
De Villiers, M. (2009). To teach definitions in geometry or teach to define. Colección Digital Eudoxus, 1(2).
Hershkowitz, R. (1987). The acquisition of concepts and misconceptions in basic geometry - or when "A little learning is a dangerous thing". In J. D. Novak (Ed): Misconceptions and Educational Strategies in Science and Mathematics. Cornell University, Vol. III, pp. 238-251.
Hanna, G. (1998). Proof as explanation in geometry. Focus on Learning Problems in Mathematics, 20, 4–13.
Buchbinder, O., & Zaslavsky, O. (2018). Strengths and inconsistencies in students’ understanding of the roles of examples in proving. The Journal of Mathematical Behavior. https://doi.org/10.1016/j.jmathb.2018.06.010
Fischbein, E. & Kedem, I. (1982). Proof and certitude in the development of mathematical thinking. Proceedings of the 6th International Conference PME (pp. 128-131). Antwerp.
Haj Yahya, A., Hershkowitz, R., & Dreyfus, T. (2014). Investigating students' geometrical proofs through the lens of students' definitions. In Oesterle, S., Liljedahl, P., Nicol, C., & Allan, D. (Eds.), Proceedings of the Joint Meeting of PME 38 and PME-NA 36, Vol. 3. pp. 217-224. Vancouver, Canada.
Krause, E. F. (1973). Taxicab geometry. The Mathematics Teacher, 66(8), 695–706.
Koichu, B., & Leron, U. (2015). Proving as problem solving: The role of cognitive decoupling. The Journal of Mathematical Behavior, 40, 233–244. https://doi.org/10.1016/j.jmathb.2015.10.005
Arcavi, A., & Hadas, N. (2000). Computer mediated Learning: an example of approach. International Journal of Computers for Mathematical Learning 5: 25–45, Kluwer Academic Publishers. Netherlands.
Leung, A., Baccaglini-Frank, A., & Mariotti, M. A. (2013). Discernment of invariants in dynamic geometry environments. Educational Studies in Mathematics, 84(3), 439–460. https://doi.org/10.1007/s10649-013-9492-4
Palatnik, A., & Dreyfus, T. (2018). Students’ reasons for introducing auxiliary lines in proving situations. The Journal of Mathematical Behavior. https://doi.org/10.1016/j.jmathb.2018.10.004
Lachmy, R., & Koichu, B. (2014). The interplay of empirical and deductive reasoning in proving “if” and “only if” statements in a Dynamic Geometry environment. The Journal of Mathematical Behavior, 36, 150–165. https://doi.org/10.1016/j.jmathb.2014.07.002