JasonLion wrote:Rows, columns, and 3x3 blocks are called houses. "See" means shares a house with.
Or "see" means within "peer cells".
Well, normally there are nine rows, nine columns and nine boxes in the Sudoku puzzle. Each row, column and box contain exactly nine cells. [Also, each cell has 20 peer cells.]
Now consider your above given puzzle XY-Wing state. Rows are denoted as alphabet A to I and columns are denoted as number 1 to 9. Each cell is denoted as product of row and column, for e.g., A1 means row A and column 1.
Pivot cell D5 means row D and column 5. Pincer cell F4 means row F and column 4; and pincer cell G5 means row G and column 5. Note that pincer cell F4 shares same box as pivot cell D5 and pincer cell G5 shares same column as pivot cell D5 but both pincer cells F4 and G5 neither share same row nor same column nor same box.
Now in this case, there are cells that share box of one pincer and column of other pincer at a same time, means, that see both pincer cells at a time, i.e., [D5 also but it's pivot cell so ignore it,] E5 [and F5 but it's already solved so ignore it also] share box with pincer cell F4 and column with pincer cell G5; and G4 [, H4 and I4 but it's already solved so ignore them as well] share box with pincer cell G5 and column with pincer cell F4. therefore both pincer cells common digit must be eliminated from these cells.
To check, one of the pincer cells must contain digit 1. In each case, both E5 and G4 cells must not contain digit 1.
Hope that clarify your "see" [or peer] problem.R. Jamil