## Understanding

Post the puzzle or solving technique that's causing you trouble and someone will help

### Understanding

Is there anyone else out there that has this problem I across all the time? When I seek to find information on a solving technique, the explanation does not usually go into detail as to why this is this and why that is that. They mostly speak to logic, a logic that seems to need no explanation.
Mowpar

Posts: 4
Joined: 25 August 2016

### Re: Understanding

Short answer, there are few gifted writers working in Sudoku. The standard for accepting a new technique requires a proof, so most people focus on that, with some attention to correctness, least they get criticized, but next to no attention on making it easily understood and almost never including information on how to spot a situation where a technique applies. The one or two gifted writers that write about Sudoku tend to stick to very simple techniques described for a mass audience, while nearly all of the other descriptions were written by people working on, or near, the forefront of technique discovery. Discovering new techniques and being a good writer don't tend to go together.

JasonLion
2017 Supporter

Posts: 641
Joined: 25 October 2007
Location: Silver Spring, MD, USA

### Re: Understanding

Simple about logic in forcing chains

Logic wich rules a strong link is: if we have 2 cand. A and B, they cant both be false AND they cant both be true. Weak connection is: if we have 2 cand. A and B, they both can be false, BUT they cant both be true. And thats all. Now i hope is clear why strong conn. can be used as weak conn. and why weak conn. cant be used as strong conn. Every chain is created from alternating weak and strong links. Logic of this 2 type connections is a result of general sudoku rules . Every unit (box, column, row) must have all values from 1 to 9 and every cel is a part of 3 units, this mean: if are only 2 possibilties one must be corect, second false - strong conn. and really true cand. cant eliminating another really true cand. - weak conn. Example how it works: our starting cand is A , we start with premise that A is true -> then( weak link) B must be false-> then C must be true. If A is really true then B must be really false. If B with another cand. C connecting strong link (s) C must be really true and again really true cand. cant eliminate another really true cand. but only really false and etc. Result: is imposible to find chain wich ending on starting A and implies that A must be false. Chain if is possible to find with this contradiction is only if A is really false cand. I hope it will help better understanding someone what forcing chains are. Bye
Kristoforus

Posts: 5
Joined: 13 July 2017

### Re: Understanding

Hi Mopar, as a result of your post I have posted <An AIC Primer>.

David PB
David P Bird
2010 Supporter

Posts: 1043
Joined: 16 September 2008
Location: Middle England

### Re: Understanding

Additionally Mopar, I've put together a help file on chains (among other techniques) at http://www.philsfolly.net.au that may be worth your perusal.
Cheers, Phil
pjb
2014 Supporter

Posts: 2185
Joined: 11 September 2011
Location: Sydney, Australia