anchor.diff:  == Running the Example
   
   
  -Download and install drools-examples as described above and then execute [path]_java org.drools.examples.DroolsExamplesApp_
  - and click on "SudokuExample".
  +Download and install drools-examples as described above and then execute [path]_java org.drools.examples.SudokuExample_.
   
   The window contains an empty grid, but the program comes with a number of grids stored internally which can be loaded and solved.
   Click on "File", then "Samples" and select "Simple" to load one of the examples.
  
positive.code: hidden pair in row at [4,6] and [4,4]
  ----
  
  Click on the "Dump" button to see the state of the grid, with cells showing either the established value or the remaining  possibilitiescandidates.
  
  
  ----
  
         Col: 0     Col: 1     Col: 2     Col: 3     Col: 4     Col: 5     Col: 6     Col: 7     Col: 8
  Row 0:   2 4  7 9   2 456        4567 9   23 56  9  --- 5 ---  --- 1 ---    3  67 9  --- 8 ---     4 67
  Row 1:  12    7 9  --- 8 ---  1    67 9   23  6  9  --- 4 ---   23  67    1 3  67 9    3  67 9  --- 5 ---
  
negative.code: Rule "hidden single" fires when there is no cell with a single candidate but when there is a cell containing a candidate but   this candidate is absent from all other cells in one of the three groups the cell belongs to.
  Both rules create and insert a `Setting` fact.
  
  Rules from the largest group implement, singly or in groups of two or three, various solving techniques, as they are employed when solving Sudoku puzzles manually.
  
  Rule "naked pair" detects identical candidate sets of size 2 in two cells of a group; these two values may be removed from all other candidate sets of that group.
  
  A similar idea motivates the three rules "hidden pair in...".
  Here, the rules look for a subset of two numbers in exactly two cells of a group, with neither value occurring in any of the other cells of this group.
  This, then, means that all other candidates can be eliminated from the two cells harboring the hidden pair.
  
  A pair of rules deals with "X-wings" in rows and columns.
  When there are only two possible cells for a value in each of two different rows (or columns) and these candidates lie also in the same columns (or rows), then all other candidates for  this value in the columns (or rows) can be eliminated.
  