In mathematics education research, there are two traditional references for describing mathematical thinking: one is focused on the mathematical process and the other on coriceptual development. The well-known references of the first type are the articles of Polya [1945, 1957, 1962, 1965]. He analyzed his own experience as a mathematician. His book was written for people challenged by the task given by him. To adopt his ideas in the classroom, teachers have to change the examples to make them understandable and challenging for their children. Mason [1982] refocused on the process from the educational viewpoints. Stacey [2007] described the importance of mathematical thinking and selected twin pairs of activities - "specializing and generalizing" and "conjecturing and convincing" as follows: