Hello, the delayed choice quantum erasure experiment seems really intriguing and although many sources seem to state that the results are what has been predicted by quantum mechanics, I'm having a very hard time understanding the results conceptually. What is exactly happening that causes there to appear to be a breach in causality? Also, I was wondering if I understood it correctly that the total pattern of the signal photons is always the same, no matter what kind of setup is created for the idler photon? And finally, was this experiment a one of, or has this experiment been repeated including different variations? If so, what are those variations?