Here are two "Twin Sudoku" puzzles from the apparently now-defunct Sudoku Magazine's Sudoku Mix #1.
Quote:
"Twin Sudoku" consists of a pair of standard sudoku puzzles each with some starting digits. To get a complete solution for the twin puzzles, it is necessary to solve each twin puzzle, but the complete solution of the twin puzzles will be obtained by substituting the corresponding values of the digits from one twin sudoku into the other.
For example, in the first grid of puzzle #53, R5C5 is 9 and in the second grid, R5C5 is 3, so that in every cell in the first grid where there is a 9, the corresponding cell in the second grid will be a 3. However, a 9 in the second grid will not NECESSARILY be a 3 in the first grid (in this case, a 3 in the first grid would be a 1 in the second grid, as in R3C3).
Here are the two sets of puzzles:
#53
Code:
.............6......3.8.5.....3.2....28.9.47....8.5.....4.3.2......2.............
.6.4.2.3.7.......6..1.6.5..5.......9..6.3.7..2.......1..7.1.8..9.......3.5.7.3.1.
#54
Code:
...573....3.....4....1.4...5.4.1.2.98..957..63.6.8.5.7...7.9....8.....9....845...
..........4..5..9...7.1.5............31.2.94............3.4.6...7..6..5..........