Così fan tutte
From Longman Dictionary of Contemporary EnglishCosì fan tutteCo‧sì fan tut‧te /ˌkəʊsi fæn ˈtʊti $ kəʊˌsiː fɑːn ˈtʊteɪ/ a humorous opera by Mozart in which two men play a trick on the two sisters they love in order to test whether the women really love, them and will be faithful to them