Bjorn wrote:Even thouht it gives me the 9 in the middle block I wont get any further.

Right now I'm searching doubles and triplets to try eliminate some possibles but have done that for a while with no progress and yet again I ask for help...

Greetings

/Björn

Hi Bjorn -

Well it

is described as a hard one!

I think you're going to need to think a little more about doubles & triplets and what they can mean.

The simplest way I can think of descibing this generalised technique is as follows -

If you have

n candidates appearing in

n cells within any row, column or block, then no other cell in that row, column or block can contain any of those candidates.

This is simplest to understand when you have 2 candidates in 2 cells.

Clearly if the only possible candidates for 2 cells in a row/column/block are

a and

b, then neither

a nor

b can appear in any other cell in that row/colum/block.

Things get a little more tricky for

n >2 as there are more permutations amongst which the candidates can be placed in cells, but the technique still applies.

Consider the candidates

a,

b and

c dispersed across 3 cells.

abc|abc|abc

Clearly if the candidates for the three cells are in all cases

a,b and

c then it is obvious that no other cell can contain those candidates.

However, for this techique to work, it doesn't matter whether or not the three candidates each appear in

all of the cells.

The three cells could contain -

ab|bc|ba

The technique still applies - none of a, b or c can appear in any other cell in the row/column/block that is under investigation.

Exteding to 4 candidates, you

could have:

bd|bcd|abc|abd

Same thing applies. It's just a single rule - regardless of how it looks.

n candidates in n cells within a row/column/block - those candidates cannot appear in any other cell within that row/column/block.

What this enables us to do is to eliminate those candidates from other cells in the row/column/block.

For example -

For a group of 6 cells, you may have:

bd|bcd|abc|abd|abedf|abceg

From the first 4 cells, using just the one rule, you can eliminate a, b, c and d from the last two cells, leaving

bd|bcd|abc|abd|ef|eg