Léon Walras in the context of "General equilibrium"

William Stanley Jevons FRS (/ˈdʒɛvənz/; 1 September 1835 – 13 August 1882) was an English economist and logician.

Irving Fisher described Jevons's book A General Mathematical Theory of Political Economy (1862) as the start of the mathematical method in economics. It made the case that economics, as a science concerned with quantities, is necessarily mathematical. In so doing, it expounded upon the "final" (marginal) utility theory of value. Jevons' work, along with similar discoveries made by Carl Menger in Vienna (1871) and by Léon Walras in Switzerland (1874), marked the opening of a new period in the history of economic thought. Jevons's contribution to the marginal revolution in economics in the late 19th century established his reputation as a leading political economist and logician of the time.

The Lange model (or Lange–Lerner theorem) is a neoclassical economic model for a hypothetical socialist economy based on public ownership of the means of production and a trial-and-error approach to determining output targets and achieving economic equilibrium and Pareto efficiency. In this model, the state owns non-labor factors of production, and market simulations are used by the planning organs to allocate final goods and consumer goods. The Lange model states that if all production is performed by a public body such as a democratic state, and there is a functioning price mechanism, this economy will be Pareto-efficient, like a hypothetical market economy under perfect competition. Unlike models of capitalism, the Lange model is based on direct allocation, by directing enterprise managers to set price equal to marginal cost in order to achieve Pareto efficiency. By contrast, in a capitalist economy, private owners seek to maximize profits, while competitive pressures are relied on to indirectly lower the price; this discourages production with high marginal cost and encourages economies of scale.

This model was first proposed by Oskar R. Lange in 1936 during the socialist calculation debate, and was expanded by economists like H. D. Dickinson and Abba P. Lerner. Although Lange and Lerner called it "market socialism", the Lange model is a form of centrally planned economy where a central planning board allocates investment and capital goods, while markets allocate labor and consumer goods. The planning board simulates a market in capital goods by a trial-and-error process first elaborated by Vilfredo Pareto and Léon Walras. The Lange Model is in practice a type of centrally planned economy and not a type of market socialism.