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Eternity II

Reduce the search

Pruning, propagation, invariants and necessary conditions: everything that throws away hopeless states before the search wastes time on them.

Why it's hard

finding
Why a faster computer doesn't help
finding
Forbidden patterns
finding
No forced moves
finding
Where you place the hints beats how many
finding
Piece theft, where solvers die
finding
The border balance

Build a solver

concept
Arc consistency, from AC-3 up
concept
All-different, Régin's matching filter
concept
Edge slipping
concept
No-good learning: remembering why you failed
concept
Fill orders
concept
Restarts and heavy tails
concept
When learning collapses
concept
Parity arguments
reference
Dead ends

The lab

experiment
CSP presets, measured
experiment
LODESTONE
page
The DFS study
page
What each idea buys
page
The hint study
page
How the study is built
page
What the study found
page
The repair study
page
What each decision buys

History & community

papers
Papers

Neighbouring roads

All nine roads
Why it resists

The design tuned to be unsolvable, and the walls that prove it.

Backtracking

DFS done seriously: fill orders, restarts, break indices.