DISCOVER

## Video transcription

I'm showing you tips and techniques in solving Soduku puzzles. Our next master technique is called forcing chains. A good way to start in this example is to find an option. It only has about 2 candidates. In here, you just figure okay what happens if this was a 1. If this was a 1, that would mean that this would have to be a 4. If that's a 4, then means that would have to be a 7. What it would basically mean that thru using forcing just going by here, this would have to be a 5 in this example here. On the second choice, if this is a 2 it would go in another round about way going thru all the different permutations that this will have to be a 5 as well. It's a good idea in examples like this, especially when it starts to get more advanced, is to have either another sheet of paper or a copy of the puzzle that you're working on that you can use little notes on. With this forcing chain, basically you find out that by using. It doesn't make any difference if you the 1 or the 2 here, the result for here is always the same 5. Basically that's what you're forcing. You're saying if this is a 1, you go thru the different permutations, this turns out to be a 5. If this is a 2, it also becomes a 5. Regardless of what you put here, this will be a 5. So knowing that since the puzzle is going to work out where the 1-9 will be in every single row, colum and cube, this will have to be a 5 if this is a 1 or a 2. So you basically force this number out using both of the examples here. A good way to use these is again, to have another note pad beside you so you can go thru the different permutations. But in this particular forcing chain, this ends up to be 5 regardless if you use a 1 or 2 there. In our next clip, we'll show the Japanese strategy of Nishio.