### ... by: Sherman

Andrew -

You say simpler strategies can be used in place of multi-coloring, but you do not mention what those strategies are. I loaded the second example into your solver and it ended up using an X-cycle on 9 to solve cell R6C5. Personally, I find multi-coloring on such short chains easier than hunting for a suitable X-cycle, as there is only one way to form all the colored chains for a number but many possible X-cycles on that number.

Sherman

P.S. I love this web site. I just stumbled across it a few weeks ago. It is a great companion to your book that I read way back in 2007.

### ... by: Patrice

Hi Andrew,

Nice explanations, thanks

I don't see where Multi-Coloring take place in the solver strategies

Is it merged with another strategy ?
Andrew Stuart writes:

Hi Patrice, I should have put a notice up when I stopped using thi strategy, I have now done so.

### ... by: Howard

Thank you for your lectures on Sudoku.

I think, in para. 2 under Type 1 Multi-Coloring, the number 7 can only be removed from the A+ square that can see both B+ and B- squares.

We shoulld not remove 7 from other A+ squares that can see only B+ or B- squares but not both.

Am I right?

Howard

### ... by: Howard

Thank you for your lectures on Sudoku.

I think, in para. 2 under Type 1 Multi-Coloring, the number 7 can only be removed from the A+ square that can see both B+ and B- squares.

We shoulld not remove 7 from other A+ squares that can see only B+ or B- squares but not both.

Am I right?

Howard

### ... by: Mr Turner

For an excellent discussion of the issue and the example you seek, take a look at http://www.geometer.org/mathcircles/sudoku.pdf. In particular, look at Section 9, Coloring and Multi-Coloring.

### ... by: Dino Hsu

Both type I and type II tecniques are about the interactions between one chan and another, why calling it multi-coloring instead of multi-chain?

Andrew Stuart writes:

For historical reasons, thats the name the community coined way back when. Colouring emphasises that it is easier to mark the chains with colours.