1. Ainsworth, S. (1999). The functions of multiple representations. Computers in Education, 33(2–3), 131–152.
2. Bogdan, R. C. & Biklen, S. K. (2003). Qualitative research for education: An introduction to theories and methods (4th ed.). Boston: Allyn and Bacon.
3. Cobb, P., Yackel, E. & Wood, T. (1992). A constructivist alternative to the representational view of mind in mathematics education. Journal for Research in Mathematics Education, 23(1), 2.
4. Deloache, J. S. (1989). The development of representation in young children. In H. W. Reese (Ed.), Advances in child development and behavior (Vol. 22, pp. 1–39). New York: Academic.
5. Dufour-Janvier, B., Bednarz, N. & Belanger, M. (1987). Pedagogical considerations concerning the problem of representation. In C. Janvier (Ed.), Problems of representation in the teaching and learning of mathematics (pp. 109–122). Hillsdale, NJ: Lawrence Erlbaum Associates.