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The Metropole du Grand Paris, or Metropolis of Greater Paris, formally came into existence on January 1, 2016. It is an administrative structure for cooperation between the City of Paris and its nearest suburbs. It includes the City of Paris, plus the communes, or towns of the three departments of the inner suburbs; Hauts-de-Seine, Seine-Saint-Denis and Val-de-Marne; plus seven communes in the outer suburbs, including Argenteuil in Val d'Oise and Paray-Vieille-Poste in Essonne, which were added to include the major airports of Paris. The Metropole covers 814 square kilometers and has a population of 6.945 million persons.
How many communes of the outer suburbs are included in the metropole?
seven