Larsdoku — Pure Logic Sudoku Solver

Every Puzzle.
Pure Logic.

Six techniques that changed how we solve expert Sudoku. No guessing. No backtracking. Every step proven by contradiction.
1,465
Top1465 Solved
0
Zone Deductions
55,862
Total Steps
Open Larsdoku Solver Open HYPERSIRO Research
Scroll to explore ↓
The Breakthrough
Six techniques the world hadn't seen.
Classic solvers stall on the hardest puzzles. X-Wing, Swordfish, Coloring — all exhausted. These four techniques pick up where everything else stops.
♦
Placement

FPC Placement

Finned Pointing Chains detect pointing patterns with a fin cell that forces a hidden single. A visual, human-friendly technique — spot the pointing pair, notice the fin, place the digit. No elimination needed.

8,365 placements · 15.0% of all steps · 653 puzzles
×
Elimination

FPC Elimination

Generalized contradiction testing. Assume a candidate is true, propagate through L1+L2 logic — if a contradiction emerges, that candidate is eliminated. The single most powerful technique in the pipeline.

9,851 eliminations · 17.6% of all steps · #1 technique
↔
Bilateral

Depth-2 Bilateral

Pick a bi-value cell. Branch on each candidate and run the full FPCE engine on both branches. Any elimination that appears in every branch is proven — a two-level proof by exhaustion.

1,336 eliminations · Reduced unsolved from 248 → 49
☆
Final Backstop

Full Pipeline Forcing

The ultimate technique. Branch on each candidate in a cell, run the entire solver pipeline on each branch. If all but one lead to contradiction, the survivor is proven.

50 firings · Eliminated all remaining 49 unsolved puzzles
›
Chain Logic

Forcing Chains

Pick a bivalue or trivalue cell. Branch on each candidate and propagate — if every branch forces the same conclusion, that conclusion is proven. Cleaner and faster than Nishio, with full contradiction tracing.

1,274 steps · 2.3% of all steps · L4 technique
◊
Network Logic

Forcing Nets

The wider sibling of Forcing Chains. Branch on cells with 3–4 candidates, propagate deeper through the constraint network. When all branches converge on the same elimination — it’s proven across the entire possibility space.

437 steps · 0.8% of all steps · L5–L7 technique
Architecture
The solver pipeline.
Each technique fires only when everything above it has stalled. The pipeline escalates from simple to profound — and never needs to guess.
L1 Singles
→
L2 Pairs
→
FPC Placement
→
FPCE
→
L3–L5
→
L6+
→
D2B
→
FPF
→
Zone Deduction
100%
Pure Logic — Zero Guessing

Tested against all 1,465 puzzles in the Top1465 benchmark — the hardest known set. Verified across 100 symmetry-shuffled variants per puzzle. Every placement proven by contradiction. Every elimination traceable.

35.1%
Steps from new techniques
13+
Classic techniques made obsolete
1.2T
Shuffle variants per puzzle

“For each candidate it can only be ON or OFF — so if you try both then you are not guessing anymore, just being logical and thorough.”

— Andrew Stuart, creator of SudokuWiki.org
Try it yourself.

Import any puzzle. Watch the pipeline solve it step by step.

Open Larsdoku Solver pip install larsdoku