Mirrored from Sudopedia, the Free Sudoku Reference Guide
In this picture we can delete the 1's in the yellow cells. There is a strong link at diagonal R1C9-R9C1 (only two cells with candidate 1) a weak link between R2C2 and R2C8 (in the same line) and no more 1's at the diagonals.
Now there is no candidate 1 in R7C7. Again we have fins in the orange cells (not both are necessary), the strong link on diagonal R1C9-R9C1, the weak link in R2 and no more 1's at the diagonals. We can also delete the 1's in the yellow cells.