However, in principle, eliminating a possible value for a given cell may require some indirect reasoning, i.e. the chaining of reasoning steps. Some examples of these kind of cases from the sample puzzles supplied with the program are given below.
Here is how to read the color-coded board indicators in conjunction with the two messages shown.
[Click here for a
larger version of the diagram.]
Assuming (3,7) is 3 (highlighted in red with a circle) results in an inconsistent board. If that is true, (3,7) cannot be 3 and the offending possibility can be removed.
Making the assumption (3,7)=3 results in (8,5) and (9,5) both having
the value 6, which, of course, is inconsistent, as
the two sixes are in the same column, namely 5.
Let's take each case separately.
(In what follows, red is used for contradicting values, blue for pivotal values in the chain of inference, and orange for values that will be eliminated along the way.)
Subparts of the reasoning are as follows: