Mancur Olson, and others not specifically advancing anti-socialists positions have shown that prevailing economic models upon which such democratic or market socialism models might be based have logical flaws or unworkable presuppositions. The ownership of the means of production can be based on direct ownership by the users of the productive property through worker cooperative; or commonly owned by all of society with management and control delegated to those who operate/use the means of production; or public ownership by a state apparatus. Public ownership may refer to the creation of state-owned enterprises, nationalisation, municipalisation or autonomous collective institutions. Some socialists feel that in a socialist economy, at least the "commanding heights" of the economy must be publicly owned. Economic liberals and right libertarians view private ownership of the means of production and the market exchange as natural entities or moral rights which are central to their conceptions of freedom and liberty and view the economic dynamics of capitalism as immutable and absolute, therefore they perceive public ownership of the means of production, cooperatives and economic planning as infringements upon liberty. Management and control over the activities of enterprises are based on self-management and self-governance, with equal power-relations in the workplace to maximise occupational autonomy. A socialist form of organisation would eliminate controlling hierarchies so that only a hierarchy based on technical knowledge in the workplace remains. Every member would have decision-making power in the firm and would be able to participate in establishing its overall policy objectives. The policies/goals would be carried out by the technical specialists that form the coordinating hierarchy of the firm, who would establish plans or directives for the work community to accomplish these goals. The role and use of money in a hypothetical socialist economy is a contested issue. Nineteenth century socialists including Karl Marx, Robert Owen, Pierre-Joseph Proudhon and John Stuart Mill advocated various forms of labour vouchers or labour credits, which like money would be used to acquire articles of consumption, but unlike money they are unable to become capital and would not be used to allocate resources within the production process. Bolshevik revolutionary Leon Trotsky argued that money could not be arbitrarily abolished following a socialist revolution. Money had to exhaust its "historic mission", meaning it would have to be used until its function became redundant, eventually being transformed into bookkeeping receipts for statisticians and only in the more distant future would