Notes on a ‘Constructive Proof of the Existence of a Collateral Equilibrium’

Abstract

In an interesting article in this journal, Ma (Comput Econ 45:1–30, 2015), claims that a constructive proof of existence of a Collateral Equilibrium (with a Leontief utility function) is provided in the paper. Moreover, there is also the additional claim that ‘on the basis of this proof, we can (and we shall) develop an algorithm for computing that equilibrium’ (ibid, p. 1). Thirdly, the statements that ‘the algorithm is shown by simulation to be effective’, and its effectiveness is demonstrated by ‘the accuracy of the equilibrium it provided’. These claims are, from a recursion theoretic (or computability theory) point of view, meaningless.