Designed by Erno Rubik 1983; left purchased circa 1985; right purchased 2009.
(plastic, 1.5 inches high by 2.25 inches square)
Put the numbers in order on both sides.
Notation: R for a flip of the right side, U, D for clockwise rotations of the up and down faces (- for counterclockwise, and 2 to do it twice). We also use M to denote rotating the whole puzzle 90 degrees clockwise (with respect to looking down), as a convenience so that only right flips are needed (easier to hold and also useful for the solution to Rubik 3x3x4).
Move pieces to their correct layers:
1. Repeatedly position pairs of edges on the wrong layers on the right and do R.
2. Repeatedly position two corners on the wrong layers at the front right and do:Exchange UFR and DFR: R U R U- RSolve the two layers independently:
3. Use this to permute corners; X = Step 2 transformation, Y = reverse of X:Exchange URF and URB: X M- Y D-4. Use this to permute edges:Exchange UF and UR: (R U)2 (R U2)2 XJaap's Page presents the transformations above (and others), as well as the following transformation to change a side to its mirror image (F denotes a front flip):
Jaap's Page, from: http://www.jaapsch.net/puzzles/domino.htm
McFarren's Page, from: http://www.geocities.com/abcmcfarren/math/rdml/rubdom1.htm