Multi Step Logic to Solve Sudokus
With the uncouth term "Multi Level Logic" or "Multi Step Logic" I describe all methods where you have to remember intermediate results.
Here is a little example:
- An extract from a Sudoku. The Three can only be placed with multi-level logic.
We can place a three in the extract above, though there is only one Three given.
We take a look at the left hand side 3x3 sub grid:
- In the left hand side 3x3 sub grid the Three can't be in the leftmost column.
In that 3x3 subgrid the Three can be placed in the middle row:
- In the leftmost 3x3 sub grid the Three can only appear in two cells, both in the same row.
With that knowledge we can conclude that the Three can't be in the second row in any of the other of the shown 3x3 sub grids.
- In the middle 3x3-Block has to be a Three. It can't be in the second row, since that is already occupied - even if don't know exactly where.
Only one free cell remains for the Three:
- The extract of the Sudoku with our newly found Three.