generally quite uncommon. The second form of exchange within elementary structures is called generalised exchange, meaning that a man can only marry either his MBD (matrilateral cross-cousin marriage) or his FZD (patrilateral cross-cousin marriage). This involves an asymmetric exchange between at least three groups. Matrilateral cross-cousin marriage arrangements where the marriage of the parents is repeated by successive generations are very common in parts of Asia (e.g. amongst the Kachin). Lévi-Strauss considered generalised exchange to be superior to restricted exchange because it allows the integration of indefinite numbers of groups. Examples of restricted exchange are found, for instance, in the Amazon basin. These tribal societies are made up of multiple moieties that often split up, rendering them comparatively unstable. Generalised exchange is more integrative but contains an implicit hierarchy, as e.g. amongst the Kachin where wife-givers are superior to wife-takers. Consequently, the last wife-taking group in the chain is significantly inferior to the first wife-giving group to which it is supposed to give its wives. These status inequalities can destabilise the entire system or can at least lead to an accumulation of wives (and in the case of the Kachin, also of bridewealth) at one end of the chain. From a structural perspective matrilateral cross-cousin marriage is superior to its patrilateral counterpart; the latter has less potential to produce social cohesion since its exchange cycles are shorter (the direction of wife exchange is reversed in each successive generation). Lévi-Strauss' theory is supported by fact that patrilateral cross-cousin marriage is in fact the rarest of three types. However, matrilateral generalised exchange poses a risk as group A depends on receiving a woman from a group that it has not itself given a woman to, producing a less immediate obligation to reciprocate compared to a restricted exchange system. The risk created by such a delayed return is obviously lowest in restricted exchange systems. Lévi-Strauss proposed a third structure between elementary and complex structures, called semi-complex structure or Crow-Omaha system. Semi-complex structures contain so many negative marriage rules that they effectively prescribe marriage to specific parties, thus somewhat resembling elementary structures. These structures are found, for example, among the Crow Nation and Omaha Native Americans in the United States. In Lévi-Strauss' view, the basic building block of kinship is not just the nuclear family, as in structural-functionalism, but the so-called kinship atom: the nuclear family together with the wife's brother. This "mother's brother"