I am relatively new to Sudoku and although I have read quite a lot of math I seem to struggle with some of the more advanced techniques. I have read several explanations but I just don't get most of them. So I have solved a hard one as far as I can and barring simple oversight the following example will now need a technique I don't know how to apply.

Some of the techniques that leave me with a blank stare after reading about them are "x-wing", "swordfish" and "solving with colours". Whatever is needed I hope this concrete example will help me understand the technique better (and if it doesn't I can bug you with more questions here). Hopefully I won't have missed any pairs or triples although I have trouble spotting quads at (most) times.

So, what would be the next technique to use here? Start with one if there are multiple ones, or I will get an even bigger headache than I have now.

Thank you in advance if you take the time to help me out.

- Code: Select all
`Start: Current: Candidate numbers:`

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|83.|9..|...| |83.|9.6|..4| [],[],[125] [],[15],[] [27],[257],[]

|...|.23|9.1| |..4|823|9.1| [67],[567],[] [],[],[] [],[567],[]

|9..|7..|..8| |9..|7.4|..8| [],[1256],[1256] [],[15],[] [236],[2356],[]

|-----------| |-----------|

|...|...|..7| |..9|5..|..7| [126],[1268],[] [],[46],[28] [1346],[1346],[]

|.4.|3.9|.8.| |.4.|3.9|582| [167],[],[16] [],[67],[] [],[],[]

|5..|...|...| |5.3|1..|..9| [],[2678],[] [],[467],[28] [346],[346],[]

|-----------| |-----------|

|3..|..1|..5| |3..|.91|..5| [],[268],[268] [24],[],[] [478],[47],[]

|4.7|68.|...| |497|685|..3| [],[],[] [],[],[] [12],[12],[]

|...|..7|.96| |...|.37|.96| [12],[1258],[1258] [24],[],[] [48],[],[]

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(This is websudoku's evil #8,483,179,112)