1. Mental effort and errors in bracket expansion tasks;Ayres,2000
2. Barcellos, A. (2005). Mathematical misconceptions of college-age algebra students. Unpublished dissertation. University of California, Davis.
3. Barnes, H. (2006). Effectively using new paradigms in the teaching and learning of mathematics: Action research in a multicultural South African classroom. Retrieved from http://209.85.165/search?q=cache:QFp1nAAMGuekJ:math.unipa.it/∼grim/SiBarnes,PDF+Effectively+using+new+paradigms&hl=el&ct=clnk&cd=1
4. Early algebra and algebraic reasoning;Carraher,2007
5. The problem of concatenation in early algebra;Chalouh,1983