the ‹ › buttons were a fourth way of getting around, next to zoom in, zoom out and the swipe, and the only one with buttons. what they did is look at the same pieces grouped another way. cube design already has a way to do that: a grouping is a piece too. "apps" is a piece of the violations cube; zooming into it shows its pieces (anlat, cubes, mosaic, cube design), and zooming into anlat shows the violations seen there. nothing new was needed, so the buttons were a navigation system invented on the spot, and the colour key under them was a legend explaining a picture, which a piece you can open does not need.