by Kristoforus » Sun Jul 30, 2017 12:07 pm
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