Article 83 (Requisites for compulsory purchase) The law shall lay down the means and forms of intervention in relation to, and for the public appropriation of, means of production, together with the criteria for setting the applicable compensation. Article 84 (Public domain) 1. The following belong to the public domain: a) Territorial waters, together with their beds and the adjacent seabeds, and lakes, lagoons and watercourses that are suitable for navigation or flotation, together with their beds; b) Airspace over Portuguese territory, above the recognised limit for proprietary or surface rights; c) Mineral deposits, mineral and medicinal water sources and natural subterranean cavities below the ground, save for rocks, ordinary earth and other materials that are habitually used for construction; d) Roads; e) National railway lines; f) Other property that is classified as such by law. 2. The law shall define what property forms part of the public state domain, the public domain of the autonomous regions and the public domain of local authorities, as well as the regime, terms and conditions of use and limits governing it. Article 85 (Cooperatives and worker-management experiments) 1. The state shall stimulate and support the creation and activities of cooperatives. 2. The law shall define the fiscal and financial benefits to be enjoyed by cooperatives, as well as preferential terms and conditions for obtaining credit and technical assistance. 3. The state shall support viable worker-management experiments. Article 86 (Private enterprises) 1. The state shall encourage entrepreneurial activity, particularly that of small and medium-sized enterprises, and shall inspect fulfilment of the respective legal obligations, especially by enterprises that engage in activities that are of general interest to the economy. 2. The state may only intervene in the management of private enterprises on a transitional basis, in cases that are expressly provided for by law and, as a general rule, subject to prior judicial decision.