of the place of habitual residence to establish that he did not give a free consent. Formal validity Under Article 9, a contract concluded between persons who are in the same country is formally valid if it satisfies the formal requirements of either the Applicable Law or the law of the country where it is concluded. A contract concluded between persons who are in different countries is formally valid if it satisfies the formal requirements of either the Applicable Law or the law of one of those countries. Where a contract is concluded by an agent, the country in which the agent acts is the relevant country for the purposes of the earlier tests. But a contract relating to immovable property is always subject to the mandatory provisions of the lex situs. Transfers of obligation Article 12 deals with a voluntary assignment or novation. Whether the rights and/or obligations can be transferred, the nature of the relationship between the assignee and the debtor that results from a transfer, the conditions under which the assignment can be invoked against the debtor, and any question whether the debtor's obligations have been discharged, are determined by the Applicable Law of the original agreement. The Applicable Law of the transfer will determine the mutual obligations of assignor and assignee as against the third party, i.e. "the debtor". Article 13 deals with subrogation so that whether a third person may enforce an existing liability owed to a "creditor" by a "debtor" is determined by reference to the law which governs the debtor's duty to satisfy the creditor. Ordre public Under Article 16, the forum court may invoke its own public policy as a justification for refusing to apply the lex causae. Composite or federated states Under Article 19, where the choice of law rules point to a country with more than one legal system, the Convention selects the most appropriate municipal law (not the choice of law rules of that law given that renvoi is excluded). Signature, ratification and amendment The convention was signed by Belgium, Germany, France, Ireland and Italy, Luxembourg and the Netherlands on 19 June 1980, followed by Denmark and the United Kingdom in 1981, thus covering all members of the European Communities. It entered into force in 1991 for 8 of those countries and one year later for Ireland. During the enlargement of the Communities with Greece (1984), Spain and Portugal