Handling Defeasibilities in Action Domains

Representing defeasibility is an important issue in common sense reasoning. In reasoning about action and change, this issue becomes more difficult because domain and action related defeasible information may conflict with general inertia rules. Furthermore, different types of defeasible information may also interfere with each other during the reasoning. In this paper, we develop a prioritized logic programming approach to handle defeasibilities in reasoning about action. In particular, we propose three action languages {\cal AT}^{0}, {\cal AT}^{1} and {\cal AT}^{2} which handle three types of defeasibilities in action domains named defeasible constraints, defeasible observations and actions with defeasible and abnormal effects respectively. Each language with a higher superscript can be viewed as an extension of the language with a lower superscript. These action languages inherit the simple syntax of {\cal A} language but their semantics is developed in terms of transition systems where transition functions are defined based on prioritized logic programs. By illustrating various examples, we show that our approach eventually provides a powerful mechanism to handle various defeasibilities in temporal prediction and postdiction. We also investigate semantic properties of these three action languages and characterize classes of action domains that present more desirable solutions in reasoning about action within the underlying action languages.Comment: 49 pages, 1 figure, to be appeared in journal Theory and Practice Logic Programmin

Externalities, income taxes and indeterminacy in OLG models

Using an aggregate two-periods overlapping generations model with endogenous labor, consumption in both periods of life, homothetic preferences and productive external effects [Lloyd-Braga et al., 2007. Indeterminacy in dynamic models: When Diamond meets Ramsey. Journal of Economic Theory 134, 513-536], we examine the effects of alternative government financing methods on the range of values of increasing returns leading to indeterminacy. We show that under a large enough share of first period consumption over the wage income, local indeterminacy can easily occur for mild externalities if constant government expenditure is financed through either labor or capital income taxes. More precisely, we show that, with labor income taxes and mild externalities, small government expenditures are helpful to local indeterminacy, while large government expenditures are useful to stabilize the economy. With capital income taxes and mild externalities, local indeterminacy always exists. Moreover, we explore how our previous results are changed once government expenditure is endogenously determined for fixed rates on labor and capital income under the balanced-budget rule.Indeterminacy; Endogenous income tax rates; Externalities.

Are Progressive Income Taxes Stabilizing? : A Reply

Dromel and Pintus [Are Progressive Income Taxes Stabilizing?, Journal of Public Economic Theory 10, (2008) 329-349] have shown that labor-income tax progressivity reduces the likelihood of local indeterminacy, sunspots and cycles in a one sector monetary economy with constant returns to scale. In this note, we extend Dromel and Pintus (2008) into a two sector monetary economy with constant returns to scale studied by Bosi et al. (2007) and reassess the stabilizing effect of progressive income taxes. We show that the result in Dromel and Pintus (2008) is robust to this extension, which means that changes of the production structure won't affect the stabilizing effect of progressive income taxes, i.e., tax progressivity (regressivity) reduces (increases) the likelihood of local indeterminacy, sunspots and cycles.Tax Progressivity, local indeterminacy

Endogenous income taxes and indeterminacy in dynamic models: When Diamond meets Ramsey again.

This paper introduces fiscal increasing returns, through endogenous labor income tax rates as in Schmitt-Grohe and Uribe (1997), into the overlapping generations model with endogenous labor, consumption in both periods of life and homothetic preferences (e.g., Lloyd-Braga, Nourry and Venditti, 2007). We show that under numerical calibrations of the parameters, local indeterminacy can occur for distortionary tax rates that are empirically plausible for the U.S. economy, provided that the elasticity of capital-labor substitution and the wage elasticity of the labor supply are large enough, and the elasticity of intertemporal substitution in consumption is slightly greater than unity. These indeterminacy conditions are similar to those obtained within infinite horizon models and from this point of view, Diamond meets Ramsey again.Indeterminacy; Endogenous labor income tax rate.

Endogenous income taxes in OLG economies: A clarification

This paper introduces endogenous capital income tax rates as in Schmitt-Grohe and Uribe (1997), into the overlapping generations model with endogenous labor and consumption in both periods of life (e.g., Cazzavillan and Pintus, 2004). In contrast with the previous result that the existence of endogenous labor income taxes raises the possibility of local indeterminacy (Chen and Zhang 2009), it shows that increasing the size of capital income taxes can make shrink the range of values of the consumption--to--wage ratio associated with local indeterminacy, because of two conflicting effects on savings that operate through wage and interest rate.Indeterminacy; Endogenous capital income tax rate.

Tariff and Equilibrium Indeterminacy--A Note

We explore the equivalence between the factor income taxes (in Schmitt-Grohe and Uribe 1997) in the closed economy and the tariff in the open economy, in the sense that they share similar propagation mechanism of sunspot and fundamental shocks under a balanced-budget rule.Sunspots; Endogenous Tariff Rate; Comovement