Jasper32 wrote:BTW, I found the easiest method method was to use the "Pattern Elimination"...

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`+-----------------------------------+ `

| . 5 . | -5 5 . | . 5 . |

| . . 5 | 5 5 . | . . . |

| . 5 5 | . . . | . 5 . |

|-----------+-----------+-----------|

| . . . | . . . | 5 . . |

| . . 5 | 5 . . | . . . |

| . 5 . | . 5 . | . . . |

|-----------+-----------+-----------|

| 5 . . | . . . | . . . |

| . . . | . . 5 | . . . |

| . . . | . . . | . . 5 |

+-----------------------------------+

Eventually you may want to learn about Alternating Inference Chains (AIC) that describe the underlying logic of many “patterns.” For the above grid position, the elimination of interest can be derived from a very simple AIC (also known in this case as a grouped X-chain or a grouped Turbot fish):

(5): r5c4 = r5c3 – r2c3 = r2c45 => r1c4 <> 5.

The “=” and “-” symbols refer, respectively, to strong and weak inference between the 5s in each indicated cell (or cell group). The chain starts and ends with a strong-inference link. Any other candidate that can “see” (weakly link to)

both ends of the chain can be eliminated. In this case, (5)r1c4 can “see” (5)r5c4

and both of the 5s in cell group r2c45. (5)r1c4 can therefore be eliminated. [

Edit to add: This AIC, which is in Eureka notation, is equivalent to the chain already provided by

daj95376 at the end of page 1.]

If interested, you can read up on inference, links and AICs in both Sudopedia and in this forum at:

http://forum.enjoysudoku.com/viewtopic.php?t=3865.