Reversors and Symmetries for Polynomial Automorphisms of the Plane

We obtain normal forms for symmetric and for reversible polynomial automorphisms (polynomial maps that have polynomial inverses) of the plane. Our normal forms are based on the generalized \Henon normal form of Friedland and Milnor. We restrict to the case that the symmetries and reversors are also polynomial automorphisms. We show that each such reversor has finite-order, and that for nontrivial, real maps, the reversor has order 2 or 4. The normal forms are shown to be unique up to finitely many choices. We investigate some of the dynamical consequences of reversibility, especially for the case that the reversor is not an involution.Comment: laTeX with 5 figures. Added new sections dealing with symmetries and an extensive discussion of the reversing symmetry group

Assessing Euro-Med Trade Preferences: The Case of Entry Price Reduction

The EU protects some of its fruits and vegetables through the entry price system. This system consists on a two-tiered tariff, with high-priced exports paying an ad valorem tariff, whereas low-priced exports pay also a supplementary specific tariff. The breaking point between high and low export prices is the entry price level decided by the EU, generally the same level for all third countries. In a few cases, some Southern Mediterranean partners of the EU have agreed a reduced entry price for their exports, together with the more common ad valorem tariff reduction. Among the indicators used for gauge the value of preferences, there is no one devoted to this case of reduced entry price, hence we develop a new indicator that allows to split which part of the preferential gains corresponds to the entry price reduction and which part corresponds to the "usual" ad valorem tariff reduction. We apply this methodology to Moroccan clementines trade flows, with two main findings: 1) The entry price reduction ranges up to 39% of the economic value of preferences in some months; 2) Morocco is not maximizing the gains due to this reduction, and could take some trade and policy lessons, mainly trying to better fit to the concession or, if impossible, use it as negotiating capital in future reviews of the agreement.International Relations/Trade,