To a large extent, it lies, no doubt, in what is presented in this work under the title of meta lever, a method which it is certainly interesting to develop and further refine. There exists in mathematics courses a strange prudery which forbids one to ask questions such as, Why are we doing this? -, At what is the objective aimed? -, whereas it is usually easy to reply to such questions, to keep them in mind, and to show that one can challenge these questions and modify the objectives to be more productive or more useful. If we don t do this we give a false impression of a gratuitous or...