This is an old technique that has been used in fields as far ranging as painting, music, and religion.

"Di" means two, and "ptycohs" means "folded over," (and of course "tri" means three.) It's basically the phenomenon that when you look at two pics side by side they take on new meaning than if you looked at them seperately. The two combined to be more than each alone. It's an interplay between images to evoke a feeling.