“No great collection was ever formed without a dealer,” said Gil Edelson, when he was vice president of the Art Dealers Association of America. This is certainly true of the enigmatic dealer Paul Guillaume, whose Impressionist and École de Paris collections—still among the finest that exist, with works by Matisse, Picasso, and Modigliani—are among the holdings of the Musée de l’Orangerie. On the occasion of the Yokohama Museum of Art’s 30th anniversary, 70 masterworks from the Musée are being shipped from Paris for a major showing in Japan. —E.C.