E. Yackel, and P. Cobb. Nineteenth International Conference for the Psychology of Mathematics Education, page 264-271. Recife, Brazil, Program Committee of the 19th PME Conference, (1995)
M. Sasman, A. Olivier, and L. Linchevski. Fifth Annual Congress of the Association for Mathematics Education of South Africa, 1, page 177-182. Port Elizabeth, Port Elizabeth Technikon, (1999)