HP__ Solving “hardest puzzles”


This new chapter is an attempt to summarize one year of work on hardest puzzles.

Up to now, hardest puzzles have been shown in these 2 threads


The hardest sudokus

The hardest sudokus (new thread)


I have also a nice collection of “hardest” not published generated by coloin.

A prerequisite to enter this chapter is to be aware of 




Full Tagging  not directly used in that chapter, but the background for my solver

  (in my website, some points summarized here have already been discussed)


More important is to be familiar with


Allan Barker model

Local Area Sets and Three Dimensional Sudoku the presentation made by Allan on the player’s forum


Most of the new findings are derived form that model . Moreover, although we will limit us to rank 0 logic or nearly rank 0 logic, the use of XSUDO, the free program offered by Allan Barker is a must to check eliminations possible thru a “SLG”


Several threads on the new  player’s forum contain key information and many examples of  the logic that can be applied to crack hardest puzzles.


The Illusion of Fata Morgana

bi bi pattern in hardest puzzles

Great Monster Loops

More Monster Loops, Structure and Symmetry

AIC's net equivalent to forcing net

Almost Fishes patterns


Another topic seen in that chapter is the symmetry of given. That issue has been discussed mainly in these threads.


About Red Ed's Sudoku symmetry group

Down Under Upside Down - a Sudoku puzzle



I ‘ll edit that post later to introduce links to txt files containing files of “hardest” having specific properties.