Vidarino,

Ah yes, A = B implies B = A. Dang computers, you have to spell out everything for them

Here is another little trick that may be of use to your program

.

For example, our r2c2 cell contains (1b 8e 9c). That's three candidates, which means we get the following three equations

NOT 1b = 1a = 8e 9c

NOT 8e = 8abcdfg = 1b 9c

NOT 9c = 9ab = 1b 8e

Using the quoted example, remember we got three equations from the cell containing 3 candidates. But what if we have managed to derive one of these equations from other equations, and there is no "cell"?

We can still get the other two equations using the following trick

Assume we have derived 8abcdfg = 1b 9c.

Note that TRUE = 8abcdefg = 1ab = 9abc.

Thus we can say

TRUE + 8abcdfg = 1b 9c + TRUE

1ab 8abcdfg = 1b 9c 8abcdefg

cross cancelling gives you

1a = 8e 9c

also

TRUE + 8abcdfg = 1b 9c + TRUE

9abc 8abcdfg = 1b 9c 8abcdefg

cross cancelling gives you

9ab = 1b 8e

So you can alway derive the other equations from one, even without a cell to base them on.