Many ideas in mathematics are grounded in the concept of relations, that is, specified properties that link pairs of objects. The concept of relations and their characteristics is sufficiently general to refer to many different types of relations among many different types of objects. It can easily refer to the most fundamental of human relations, the kinship of people. One group that has a complex kin system is the Warlpiri who live in a desert area in Australia's Northern Territory. The system encodes their social, political, and ritual organization and behavior. For the geometrically minded, the symmetries of the square are a useful spatial analogy to the Warlpiri kin system. At a time when kin systems of this type were little understood by Westerners, the elders of Malekula explained their system to an anthropologist using diagrams traced in the sand. The discussion of the logic of kin relations began with relationships between individuals and with familiar relationships from own culture.