 The Swiss-born Honegger experimented mixing opera with oratorio in works such as "Le Roi David" (1921) and "Jeanne d'Arc au Bûcher" (1938).But the most successful opera composer of the group was Poulenc, though he came late to the genre with the surrealist comedy "Les mamelles de Tirésias" in 1947.In complete contrast, Poulenc's greatest opera, "Dialogues des Carmélites" (1957) is an anguished spiritual drama about the fate of a convent during the French Revolution.