solve

 sudoku

This has an example of what I call 'the third column'.

The game is part done and we are looking at 3's here and from this information we can find the 3 in c5r4.

Looking at Box2, we can see that the 3 in row1 means that a 3 must be in column4 or column6 of Box2.

Looking at Box5, we can see that the 3 in row6 means a 3 must be in row4 of Box5.

Looking at Box8, the 3 in row9 means that a 3 must be in c4 or c6 of Box8.

Now there's that column4 and 6 again!

So logically, if a 3 must be in c4 or c6 of Box2 and Box8 there cannot be a 3 in those columns in Box5. A 3 must be in the third column of Box5 - column5.

As we have already proved that a 3 must be in row4 of Box5 and it cannot be in c4 or c6, therefore a 3 must be in c5r4.