MXQ Adv. Sudoku
- Begin Again: Reloads the initial values.
- Run Start Grid: The initial condition has single digits in
cells which can be eliminated from its row & column.
- Reset Colors: Removes any highlighting. Useful for actions
that do not depend on highlighting: 3 & 4 cell chains.
- Row Pairs: Displays a 2nd grid with just the rows with
either 1,2 or 3 occurrences of the selected digit. More on this
later.
- Column Pairs: Displays a 2nd grid with just the columns with
either 1,2 or 3 occurrences of the selected digit. More on this
later.
- Save & Reload Grid: Allows user to save & reload at critical
moments during the solution process.
- Numeric Buttons 1-9: Highlights the cells with the selected
digit. Click 1 to highlight all cells with a 1.

### Methodology: Highlighting

- When I solved extremely difficult grids on line, I used
"manual" highlighting to clarify the strategy targets.
- The
application described here automates the highlighting using MS
Access & VBA code.
- If a target digit occurs in 2 cells in a row or column
then there is a possible 2 cell chain.
- With 2 target digits in a row or column, then there is a
possibility of x-wing. More on this later.
- With 2 or 3 target digits in a row or column, then there
is a possibility of swordfish. More on this later.