Bill Gosper's sharing of the 4x4 "nice little sliding block head exercise" got me thinking about Stewart Coffin's 4x4x4 Convolution puzzle. John Rausch shares a partially assembled Convolution on his Puzzle World website: http://www.johnrausch.com/puzzleworld/puz/img/lg/convolution_6.jpg Three pieces (#1 at 9 o'clock, #2 at 7 o'clock, #3 at 5 o'clock) need to be added to the assemblage. The black 'cubies' end up in the corners of the finished cube. Also, piece #1 and piece #3 are seriously foreshortened (what look like one-cubie extensions going to the back are actually two-cubie extensions). The number of cubies in each of the three unassembled pieces is 9 (to fit into the 27 empty spaces of the unfinished cube). Can you complete the construction in your head? Bonus: What's wrong with one of the cubies?