reduction info
List mode reduce buttons
The Reduce 1 button will try some of the easier strategies, and if they find anything, you can get one of the following messages in the help line at the bottom of the screen:
  • In row/column/box x the number n must be here
    The program has found that there is only one candidate for number n in that row, column or box.
  • In row/column/box x the numbers n1 and n2 are forming a naked pair
    This means that you can delete all other occurrences there of these two numbers.
  • In row/column/box x the numbers n1 and n2 are forming a hidden pair
    The two numbers must be in those cells - delete all other candidates.
  • In row/column/box x the numbers n1, n2 and n3 are forming a naked triplet
    Like above but with three cells - delete all other candidates.
  • In row/column x the number n can only be found in box y
    As all candidates for that number in this row/column are inside this box, all other occurrences in this box can be removed.
  • In box x the number n can only be found in row/column y
    All candidates in the box for this number are in the same row/column. This means you can remove all other occurrences in that row/column outside the box. this box can be removed.
The Reduce 2 button applies a bit more complex strategies, and the messages that you can see in the help line are:
  • Number n is forming an "X-Wing" in rows r1 and r2 - remove other n's in both COLUMNS
    The cells in a "X-Wing" are locked together with this candidate. That means you can remove all other occurrences of the candidate in the two columns.
  • Number n is forming an "X-Wing" in columns c1 and c2 - remove other n's in both ROWS
    This is the same as above - but rotated 90 degrees. You can remove all other occurrences of the candidate in the two rows.
  • Coloured chain (Rule 2): Yellow cells cannot have the value n
    An alternating colour chain is built, and this rule says that if any unit has the same colour twice, ALL those candidates which share that colour must be OFF.
  • Coloured chain (Rule 4): Yellow cells cannot have the value n
    As above, an alternating colour chain is built, and here we are looking for cells in the same unit with the same candidate that can "see" the two different colours. The candidate in these cells can be removed.
  • Coloured chain (Rule 5): Yellow cells cannot have the value n
    As above, an alternating colour chain is built, and here we are looking for cells elsewhere with the same candidate that can "see" the two different colours. The candidate in these cells can be removed.
  • XY-wing: The candidate n in cell x;y can be eliminated
    The program has found an XY-wing and located a cell that can see both wings and has the same candidate - it can be removed.
  • X-cycles (Rule 1): Remove all n's that can 'see' two different colored n's
    A chain is built where candidates are turned OFF and ON. All uncoloured candidate n that can "see" two different colours can be removed.
  • X-cycles (Rule 2): Chain shows that cell x;y must be n - remove other candidates
    As above, a chain is built, and a removed candidate is brought back again by the chain. All other candidates n in the same unit can be removed.
  • X-cycles (Rule 3): Chain shows that cell x;y cannot be n - it can be removed
    Same chain as above. A candidate that has been turned ON is turned OFF again by the chain - it can be removed.
  • A true-false chain shows that cell x;y cannot have the value n - it can be removed
    If a true-false chain ends up where it started and the cell doesn't get the same value, you can remove that candidate.
  • A forced chain shows that cell x;y cannot have the value n - it can be removed
    A chain of cells with two candidates is built. If an illegal condition appears when chosing one of them, you can remove that choice.
The Reduce 3 button applies the swordfish strategy, and the message that you can see in the help line is:
  • Uncolored candidates of n can be removed from swordfish rows/columns
    When the same candidate is found in a row-column crossing pattern, they are coloured. This candidate in uncolored cells in the swordfish rows/columns can be removed.
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