Such is indeed the meaning of the incest prohibition conceived as the establishment of a physical system in extension: one must look in each case for the part of the flow of intensity that passes through, for what does not pass, and for what causes passage or prevents it, according to the patrilateral or matrilateral nature of the marriages, according to the patrilineal or matrilineal nature of the lineages, according to the general regime of the extended filiations and the lateral alliances.