The bounded proper forcing axiom and well orderings of the reals

We show that the bounded proper forcing axiom BPFA implies that there is a well-ordering of P(ω_1) which is Δ_1 definable with parameter a subset of ω_1. Our proof shows that if BPFA holds then any inner model of the universe of sets that correctly computes N_2 and also satisfies BPFA must contain all subsets of ω_1. We show as applications how to build minimal models of BPFA and that BPFA implies that the decision problem for the Härtig quantifier is not lightface projective

Un-Reduction of Systems of Second-Order Ordinary Differential Equations

In this paper we consider an alternative approach to "un-reduction". This is the process where one associates to a Lagrangian system on a manifold a dynamical system on a principal bundle over that manifold, in such a way that solutions project. We show that, when written in terms of second-order ordinary differential equations (SODEs), one may associate to the first system a (what we have called) "primary un-reduced SODE", and we explain how all other un-reduced SODEs relate to it. We give examples that show that the considered procedure exceeds the realm of Lagrangian systems and that relate our results to those in the literature

Some Evidence of Smooth Transition Nonlinearity in Colombian Inflation

Evidence of smooth transition autoregressive (STAR) representations is found in two, out of three, time series of different measures of annual inflation in Colombia during this decade for monthly data. The STAR-type nonlinearities are asymmetric for inflation computed as the variation of CPI while for (a measure of) core inflation are symmetric. Thus, LSTAR and ESTAR models were, respectively, estimated. No evidence of nonlinearity is found for traded goods inflation. Given the local dynamic properties of the estimated LSTAR model, only positive shocks to prices could shift negative accelerating inflation rate from the upper to the lower regime. By the same token, only stochastic shocks can move the core accelerating inflation rate from the outer regime to the middle one but the explosive nature of this regime will impulse accelerating inflation rate to the outer one.nonlinearity, core inflation, regimes, logistic and exponential transition functions.

Quid pro Quo: National Institutions and Sudden Stops in International Capital Movements

The paper explores the incidence of sudden stops in capital flows on the incentives for building national institutions that secure property rights in a world where sovereign defaults are possible equilibrium outcomes. Also thepaper builds upon the benchmark model of sovereign default and direct creditor sanctions by Obstfeld and Rogoff (1996). In their model it is in the debtor country’s interest to “tie its hands” and secure the property rights of lenders as much as possible because this enhances the credibility of the country’s romise to repay and prevents default altogether. It incorporate two key features of today’s international financial markets that are absent from the benchmark model: the possibility that lenders can trigger sudden stops in capital movements, and debt contracts in which lenders transfer resources to the country at the start of the period, which have to be repaid later. The papershows that under these conditions the advice “build institutions to secure repayment at all costs” may be very bad advice indeed.

Type Soundness for Path Polymorphism

Path polymorphism is the ability to define functions that can operate uniformly over arbitrary recursively specified data structures. Its essence is captured by patterns of the form $x\,y$ which decompose a compound data structure into its parts. Typing these kinds of patterns is challenging since the type of a compound should determine the type of its components. We propose a static type system (i.e. no run-time analysis) for a pattern calculus that captures this feature. Our solution combines type application, constants as types, union types and recursive types. We address the fundamental properties of Subject Reduction and Progress that guarantee a well-behaved dynamics. Both these results rely crucially on a notion of pattern compatibility and also on a coinductive characterisation of subtyping

Downward transference of mice and universality of local core models

If M is a proper class inner model of ZFC and omega_2^M=omega_2, then every sound mouse projecting to omega and not past 0-pistol belongs to M. In fact, under the assumption that 0-pistol does not belong to M, K^M \| omega_2 is universal for all countable mice in V. Similarly, if M is a proper class inner model of ZFC, delta>omega_1 is regular, (delta^+)^M = delta^+, and in V there is no proper class inner model with a Woodin cardinal, then K^M \| delta is universal for all mice in V of cardinality less than delta.Comment: Revised version, incorporating the referee's suggestion

Gravity and extended gravity: estimating a structural model of export entry

Exporters continuously enter and exit individual foreign markets. Although a given firm's status as an exporter tends to be persistent, the set of destination countries that a firm serves changes frequently. In this paper we empirically examine the determinants of a firm's choice of destination countries and show that their export paths follow systematic patterns. We develop a model of export dynamics where firms decide in each period the countries to which they sell. Our model allows prots from each possible destination country to depend on: (a) how similar it is to the firm's home country (gravity), and (b) how similar it is to other destinations to which the firm has previously exported (extended gravity). Given the enormous number of possible export paths from which firms may choose, conventional estimation approaches based on discrete choice models are unfeasible. Instead, we use a moment inequalities approach. Our inequalities come from applying an analogue of Euler's perturbation method to a discrete choice setting. We show that standard gravity forces have a much larger influence on sunk costs than on fixed costs of exporting and that extended gravity effects can be substantial.gravity; extended gravity; export dynamics; moment inequalities