In a 9*9 SUDOKU game what is the minimal number of digits guaranteeing a unique solution?

I wish it had occurred to me sooner (before the problem was posted) but this problem could be asking for two different things:

1.  The minimum number of digits such that it is possible to place them into the grid and yield a unique solution.  (This is what I assumed the puzzle to be but with a little research this seems to be unknown.  No spoilers here but it is in the teens.)

2.  The number of digits that if this many are placed in the grid the puzzle is guaranteed to be uniquely solvable.  This is likely a large number, almost the whole grid.

Posted by Jer on 2010-01-29 15:36:31