ABSTRACT
In order to help the reader understand the problem of correspondences posed for the child in this chapter, 1 it seems useful to begin with a description of the apparatus used. That apparatus is composed of two concentric superimposed disks. Both can be turned independently of one another in either direction. The disk on the bottom has forms drawn on it; the disk on top is made of colored transparent plastic. The form disk is divided into fourths and the resulting sectors numbered 1, 2, 3, 4. On sector 1 a triangle has been drawn, on sector 2 a star, on sector 3 a square, and on sector 4 a cross. The four sectors of the colored disk are composed of different colored transparent plastic material and are lettered a, b, c, d. Sector a is red, sector b is blue, sector c is yellow, and sector d is green. Moreover, the four absolute positions that the sectors of either disk can occupy are numbered I, II, III, IV. I is at the top, II is to the right, III is at the bottom, and IV is to the left (see Fig. 2.1). Superimposed disk apparatus. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203771600/cdd8d45c-f71f-401b-b13f-75887a16c5b9/content/fig2_1_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
