Edited sentence: "  Additional countries are listed and reference to the most recent report should be made by concerned parties."  In certain exceptional cases under Article 13b, the court's mandatory return obligation is changed to a discretionary obligation, specifically, "the judicial or administrative authority of the requested state is not bound to order the return of the child if the person, institution or other body which opposes its return establishes that there is a grave risk that his or her return would expose the child to physical or psychological harm or otherwise place the child in an intolerable situation." The duty to return a child is however not abrogated by a finding under Art.13(b) but merely changes from mandatory to discretionary.In 2014, the United States declared Brazil, Mexico, Romania, and Ukraine as "Countries with Enforcement Concerns.In the primary source of interpretation for the Convention, the Explanatory Report, Professor E.Noncompliance with the terms and spirit of the Hague Convention has been a particularly difficult problem in the practical implementation of the Convention.Pérez Vera noted the following:.The case of Cuellar v Joyce was an example of the difficulties facing left-behind parents applying to the US Central Authority.The principal purpose of the Abduction Convention is to cause the prompt return of a child to his or her "habitual residence