These are shadow cubes that are shown on the cover of the book Godel, Escher, Bach: An Eternal Golden BraidI included the original Alibre part files, the .stp part files, and the .stl part files.The part named GEB shows the shadow GEB, the part named EGB shows the shadow EGB.To print these cubes, download the .stl files, although I doubt these will print nicely, as the shape doesn't seem very stable.