ABSTRACT
What makes the backtracking problem interesting is that since at all levels the need to backtrack is imposed by the facts it would seem to involve only empirical abstraction. If the subject was successful by chance, the experimenter asked him to try a second and third time, in order to judge what he understood and what he was learning. It was also necessary for the child to understand that the locomotive could not stay at the head of the train; at certain moments it had to push A or B, otherwise it would not be able to pick up the last car. Whereas partial backtracking by one end of the moving bar, or by the locomotive, means retracing in the inverse direction part of the path already traversed in the forward direction, and integrating such a subsystem of negative orientation into a positive program is consequently more difficult.
