Snyder Notation for Sudoku: A Faster Pencil Mark System

What Snyder notation records

Snyder notation is a compact way to mark candidates inside each 3 by 3 box. Instead of writing every possible shape in every empty cell, look at one shape within one box. If that shape can appear in exactly two cells in the box, mark it in those two cells. If it has one possible cell, place it as a hidden single. If it has three or more possible cells, leave it unmarked for now. The method creates a light map of the strongest box-level restrictions without filling the board with tiny symbols. In Shapedoku, the idea works exactly the same way with the triangle, heart, crescent, and other shapes. The Notes tool keeps those marks separate from final placements, and smart cleanup removes notes made impossible by a confirmed shape. The result is a board that remains easy to scan while still preserving the pairs most likely to produce progress.

Why two positions are so useful

A shape limited to two cells in one box carries useful information even when neither cell is solved. If both cells lie in the same row, that shape cannot appear anywhere else in that row outside the box. The same is true when both lie in one column. This is the logic behind pointing pairs, and Snyder notation makes those patterns visible early. Two-position marks also help you notice naked pairs, hidden pairs, wings, and chains later in the solve. The important discipline is consistency. Sweep all nine shapes through one box before moving to the next, or sweep one shape through all nine boxes. Randomly adding a few marks gives the appearance of information without creating a reliable map. Compact notes work because every missing mark has a meaning: either the shape has more than two positions in that box, or you have not completed the sweep yet. Finish the sweep so you know which interpretation is true.

Know when to expand to full candidates

Snyder notation is most effective in the opening and early middle of a puzzle. It is not a rule that you must keep forever. When singles, locked candidates, and visible pairs stop producing moves, some cells may need full candidate lists. Expand gradually rather than flooding the whole board at once. Start with the most constrained row, column, or box, especially one containing several existing Snyder pairs. Add every legal candidate to those cells, then inspect the new map for triples, wings, or chain links. On Hard and Extreme Shapedoku puzzles, this transition is normal. Compact notes help you reach the difficult position cleanly; full notes then support the deeper deduction. If a first free Hint reveals a move in an area you had not expanded, study which candidates were missing from your view. That tells you when your notation should become more detailed on future puzzles.

1. Choose one box and one shape, then check every empty cell in that box.
2. Place the shape if only one cell is legal.
3. Mark the shape only when exactly two cells are legal.
4. Repeat the sweep for all nine shapes and all nine boxes.
5. Use aligned pairs to remove that shape from the rest of the row or column.
6. Switch to fuller candidates only when compact notes no longer expose progress.