Nice Loop

Index
Nice Loop
In the example below a Nice Loop is marked. The solid lines mark the strong links between the candidate values used in the Nice Loop. The dashed lines mark the weak links. A strong links is formed when we know that if one of the marked candidates is filled in, the other marked candidate is the value of the other cell. This is the case when a candidate exists exactly twice in a group. A weak link is formed when a candidate exists more then once in a group. This means that if one of the candidats is filled in, the other cannot be that value. There are usually lots of weak links in a puzzle.

To find a Nice Loop it is usefull to mark the strong links and try to create a loop. When this feals, the loop can be closed with one weak link. It is also possible to use multiple weak links to form a Nice Loop, but that is out the scope of this article.

When cell A is a 6, cell B is a 2, cell C is a 6, cell D is a 5 and cell E is a 6. This can be proven by following the strong links. Between cell A and E, a weak link exists. This means that when cell A is a 6, cell E cannot be a 6 and vice versa. Because of the strong links, we know that if cell A is a 6, cell E is also. This is a contradiction.

We can exclude candidate value 6 from cell A.
Nice Loop