Mainstream economics is distinguished in general economics from heterodox approaches and schools within economics. It begins with the premise that resources are scarce and that it is necessary to choose between competing alternatives. That is, economics deals with tradeoffs. With scarcity, choosing one alternative implies forgoing another alternative—the opportunity cost. The opportunity cost expresses an implicit relationship between competing alternatives. Such costs, considered as prices in a market economy, are used for analysis of economic efficiency or for predicting responses to disturbances in a market. In a planned economy comparable shadow price relations must be satisfied for the efficient use of resources, as first demonstrated by the Italian economist Enrico Barone.