Puzzle methodology
How Legen generates, verifies, and publishes Sudoku puzzles.
Every published puzzle follows a deterministic path from a candidate grid to a stable Puzzle ID, a unique solution, a verified logic trace, a versioned difficulty score, and a permanent source page.
“Legen Puzzle Engine verified” means the stated givens have exactly one solution and every claimed logical step was accepted by a separate proof verifier for the published engine version. It does not mean a human expert reviewed every puzzle.
1. Candidate generation is offline.
Candidate grids are produced by an explicit offline command. A normal site build never invents a new puzzle, reads a private generator, or changes a page because of the clock or a random seed.
2. Format and uniqueness are checked first.
The engine validates all 81 cells, rejects conflicting givens, and counts solutions with a fixed search budget. Only a puzzle with exactly one solution can enter the published catalog.
3. Logic claims require proof replay.
A detector proposes a placement or candidate elimination. A separate verifier checks the target cell, digit, unit, pattern, candidates, board revision, and immutable proof shape before the step can be applied.
4. Difficulty is versioned, not guessed from clue count.
LDI v0 uses the hardest verified technique, weighted logical work, and explicit candidate eliminations. The score is bound to a named engine and LDI version; historical values are not silently rewritten.
5. Publication is a one-way projection.
The public site consumes a field-whitelisted catalog. Private corpus material, generator state, seeds, internal commitments, and holdout diagnostics are outside the client and clean-build dependency graph.
6. Corrections stay traceable.
A factual correction receives a dated note and another verified artifact. Changes to the engine, scoring formula, schema, or puzzle facts require an explicit version change rather than an invisible edit.
What this method does not claim
- It does not measure intelligence, human completion time, or a universal notion of Sudoku difficulty.
- A complete verified engine path is one valid logical path; another solver may choose a different valid path.
- No completion-time, hint, error, account, region, or other player-behavior data enters LDI v0.
- The public data sample does not expose full proof traces, private seeds, or holdout per-puzzle diagnostics.