Progress.txt for Col's SuDoku Solver
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Progress since v1.0
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- Decoupled board & control panel
- Allowed highlighting of individual number permissions
- Improved GUI
- Implemented menu system

Progress since v2.0
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- Decoupled permission matrix so that it can be edited manually
- Right mouse button now deselects (and toggles selection) of the permissions in individual cells
- Display which permission values are removed with a 'x'
- 'reset permissions' resets the matrix to the default state, using just the simple rules to derive the permissions
- Control pad is no longer always on top
- 'do all' button repeatedly applies the simple rules until there is no more possible improvement.  This completely
  solves most simple SuDoku puzzles.
- Some changes in the menu system and user interface
- Undo / redo menu options
- Added in constrictions (If all possibilities of number 'n' within box A are on the same row/column
  then you can rule out other occurrences in the same row/column outside box A)
- Added constrictions by row/column - if all possibilities are in the same box then rule out other values
  in that box.
- Added in permission reduction by unique subsets (e.g. 'N numbers found together in exactly N cells in a R/C/B and nowhere
  else in that R/C/B'. N=2,3,4)
- Added permission reduction by disjoint subsets for box,row,column
- Added permission reduction by neighbour pairs (If all the possibilities for number 'n' in a certain box share the same
  exact two columns as the possibilities for that number in another box in the same column, then remove the possibilities
  for number 'n' in both those columns in the third box.  Equivalently for boxes in the same row, and numbers
  sharing the same two rows.)
 
Progress since v3.0
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- Added the textual explanation box for all solving moves & all reductions
  : Included expanded help test, if required
- Added in 'X-Wing' method for permission reduction for each pair of R,C,B in both directions (6 tests)
- Added in 'Swordfish' method for permission reduction for R,C triplets
- Fixed 'disjoint subsets' algorithm
- Added in capability to export SuDoku puzzles to text, html and postscript formats (for printing)
- SolveIt! - Solves any SuDoku puzzle instantly using Knuth's 'Dancing Links' Algorithm (highly optimised)
- Rate the difficulty of any Sudoku puzzle on a 6-point scale
- Added in diagnostics for each puzzle (number of solutions, legality, completion tally)
- Added in full SuDoku puzzle generation algorithm, with variable difficulty levels
- Altered the GUI slightly so I could fit in more options
- Added in Nishio & forcing chains (guesswork algorithms)
- Improved board generation mechanism to use a more realistic difficulty measure.