Which opera  Pelléas et Mélisande and Die schweigsame Frau has fewer acts ?
Die schweigsame Frau Die schweigsame Frau ("The Silent Woman"), Op. 80, is a 1935 opera in three acts by Richard Strauss with libretto by Stefan Zweig after Ben Jonson's "Epicoene, or the Silent Woman".
La caverne (Méhul) La caverne ("The Cavern") is an opera by the French composer Étienne Méhul. It takes the form of a "comédie en prose" in three acts. It premiered at the Opéra-Comique, Paris on 5 December 1795. The libretto, by Nicolas-Julien Forgeot, is based on incidents from the novel "Gil Blas" by Alain-René Lesage.