Cell references: r1c1, r5c5
Sudoku players reference cells as r<row>c<col>. r1c1 is the top-left cell. r9c9 is the bottom-right. r5c5 is the centre. Rows are numbered top-to-bottom, columns left-to-right. Some books use uppercase R1C1. The standard is the same.
Pencil marks (candidates)
Small digits written in an empty cell to record which values are still possible. Two common styles:
- Positional. The digit sits where it would visually fit inside an imaginary 3×3 mini-grid inside the cell. Fastest to scan, no rewriting needed when you eliminate.
- List. Comma-separated digits, e.g.
1, 4, 7. Easier to write by hand, slower to scan.
Cage notation (killer sudoku)
Killer sudoku cages show the sum total in the top-left corner of the cage. Cells in a cage are connected by dotted borders. See killer sudoku for the full rules.
Common shorthand
r1c5=3. "place 3 in row 1, column 5"r1c5≠3. "eliminate 3 from r1c5"b4. "box 4" (boxes numbered 1–9 left-to-right, top-to-bottom){1, 4}. a candidate set; cell can only be 1 or 4r1c2-r1c5. a range of cells in the same row, used for fish patterns
Strategy names
When you see a name like "X-wing on 5 in rows 2 and 7", that translates to: there's an X-wing pattern, the candidate is the digit 5, and the two rows containing the pattern are 2 and 7. The columns hosting the elimination follow from the pattern. See the full strategy library.