Sudoku Collaboration Project: Discussion

[Milk]

Without getting pinned by any code is it not worth discussing the logical steps the code might have to make first.

*Mark each new solved square as being exclusive to it's row, column and block
*Search each row, column and block for any exclusive numbers, and mark as solved
*Search every unsolved square for any with one possible answer, and mark as solved

Here's a few more logical steps, which I find easier to describe with a picture.
The example has used the above logical steps to get where it has.



*Circled in red are possible answers exclusive to a blocks sub row/column, these numbers can be discounted from the rest of the row/column.

*This in turn reveals some pairs (circled in blue) which are exclusive to the block, so all other possibilities within those squares can be discounted. Also happens in threes and more.

There must be more, any ideas?