Voltaire was both friend and collaborator, working with Rameau on a comedy ballet and several operas. Martini was a correspondent. Boucher, Crébillon and Piron were fellow-members of a singing club: Piron co-wrote a comic opera with him. Diderot and d’Alembert had been friends, but Rameau’s disputatiousness over the Encyclopédie’s treatment of French music made good relations difficult; He had a major spat with Rousseau, who had written the entry.