which are stored and exhibited in the Sumo Museum. Organization The Japan Sumo Association is a Public Interest Incorporated Foundation since 2014. Therefore its functioning is of a non-profit organization and its activities are regulated through a top-down system of government supervision, as well as adherence to strict establishment conditions in exchange of preferential treatments under the tax system. Its operations are authorized and defined by the administrative agency of the Act on Authorization of Public Interest Incorporated Associations and Public Interest Incorporated Foundation (Act No. 49 of 2006). Professor Mark D. West defined the organization of the Association as a "complex web of formal legal rules and informal social norms" while the association's choice to apply rules or to defect to norms "is based on a calculation of comparative efficiency". In this case, "legal rules" refers to the legislative and judicials provisions as well as the organizational rules nominally approved by the Ministry of Education, as sumo's supervising agency, where social norms are traditionnal constraints not enforceable by law. The Japan Sumo Association relations between its members are primarily shaped by rules and norms related to the ownership and transfer of the "elder stocks" held by the Association elders. Of all the employees of the Association only them can manage the organization. The toshiyori kabu system Former wrestlers gain the right to participate in the functioning of the Association by inheriting a share (called a kabu), of which there are 105. The value of these shares was extremely high and rules only permited former sumo wrestlers who either reached at least a san'yaku rank (komusubi or higher) or been ranked for a significant number of tournaments as a sekitori to purchase them. Since the introduction of the Japan Sumo Association as a Public Interest Foundation, the shares were no longer purchasable, but rather collectively managed by the Association. Japanese citizenship is also a prerequisite. Each share is associated with a particular name, and in the sumo world the former wrestler will be known by that name, usually with the suffix oyakata. The members are also often called elders in English. An exception to the normal acquisition is made for the most successful rikishi, former yokozuna, who may be offered a "one generation" elder stock (called ichidai toshiyori) without having to use a traditionnal share in the Association and enter their retirement duties with their wrestling name. Since this exception