ABSTRACT
This lecture was given at the University of Bahia, Brazil, on 1st November 1976. It was first published in two parts in Barbárie, No. 4, été 1981, 23–7 and No. 5, été 1982, 34–42. It first appeared in French in Dits et écrits, Vol. IV, 182–94, followed by a discussion to 201. The discussion is not translated here.
