Griddlers Tutorial - Solving Puzzles
Example 4: Complex Logic (a)
Here is an excellent example of a more complex type of logic.
|  | First, fill in as much of the puzzle as you can using simple logic. That's not very much. :-) | 
|  | Now let's look at the square circled in green. We can see by the column clues that it must be either in a group of "1" or a group of "2". Let's see what the two possibilities would look like. | 
|  | This is what the puzzle would look like if that square is a "1" clue. | 
|  | This is what the puzzle would look like if that square is part of clue 2. You can see we would have to put 3 single squares below the group of two and this is the only possible formation. | 
|  | You can see that either way the square marked with a red dot must be in white. | 
