An economic system, which consists of a number of relationships among the relevant factors, is modelled as a system of equations or inequalities of certain unknowns, whose solution represents a specific state in which the system settles. This is typically exemplified by the Walrasian competitive economy (Walras, 1874), consisting of the interaction of manifold behaviours of many individual agents with different motivations, whose specific state is a competitive equilibrium in which certain prices of goods solve the system of equations representing the simultaneous clearing of all the markets of goods so as to make those individual behaviours mutually consistent.