I was very familiar with the traditional Irish air "Moreen" ("Minstrel Boy" is based on this air) since my school boy days and I was amazed when I heard Entr'acte from Bizet's Carmen for the first time. The two tune are identical in many ways. Did Bizet borrow the melody from "Moreen?" He did borrow some melodies for his masterpiece L'Arlesienne from traditional folk tune "The Three Magis."