[2] Duncker, K.: 1945, On Problem Solving, Psychological Monographs, vol. 58 (270), 1-112

[3] Polya, G.: 1957 (2nd ed.), How to solve it, Doubleday, New York

[4] Kulm, G.: 1984, The Classification of Problem-Solving Research Variables, in Goldin, G. A. and McClintock, C. E. (eds.), Task Variables in Mathematical Problem Solving, The Franklin Institute Press, Philadelphia, Pensylvania

[5] Lester, F. K.: 1980, Research on Mathematical Problem Solving, in Shumway, R. (ed.), Research in Mathematics Education, NCTM, Reston, Virginia

[6] Silver, E. A.: 1985, Research on Teaching Matematical Preoblem Solving: Some Underrepresented Themes and Needed Directions, in Silver, E. A. (ed.), Teaching and learning Mathematical Problem Solving: Multiple Research and Perspectives, Lawrence Erlbaum Associates, Hillsdale, N.J.

[7] Lester, F. K.: 1994, Musing abut Mathematical Problem-Solving Research: 1970-1994, Journal for Research in Mathematics Education, vol. 25, n. 6, 660-675

[8] Lester, F. K.: 1985, Methodological Considerations in Research on Mathematical Problem Solving Instruction, in Silver, E. A. (ed), Teaching and learning Mathematical Problem Solving: Multiple Research and Perspectives, Lawrence Erlbaum Associates, Hillsdale, N.J.