D(1,3,4,5) !=0 and D(1,2,4,5) != 9. D5 cannot be 0 (it would be lowest), D5 cannot be higher than 2 because d5(3) + d4(6) => d1(9) but d3 is highest. d5 must be 1|2, so d4 must be 2|4, so d1 must be > 3, so d3 must be > 4. D2 must be 0|1. Eliminate the impossible Digit 1 2 3 4 5 ----------------- 0 x 0 x x x 1 x 1 x x 1 2 x x x 2 2 3 x x x x x 4 4 x x 4 x 5 5 x 5 x x 6 6 x 6 x x 7 7 x 7 x x 8 8 x 8 x x 9 x x 9 x x Leaves us these choices. 4 0 5 2 1 5 1 6 4 2 6 7 7 8 8 9 d1+1 = d3 means this further reduces to 40521 50621 60721 70821 80921 * 70842 71842 80942 * 81942 *