Scroll back for the givens grid. After the fourth 4-fill, we never get back to the three unresolved 3-fills in the bypass trace. Here is the grid, just before SE6 (halfway down) wipes out the naked pairs. The Sysudoku basic level close down is complete. Many basic level example traces are reached by scrolling back.  For each example, the givens grid is one post further back. Earlier basic level examples, and advanced examples, can be located by date on Titles, and found by the monthly archive. The weekly posts are extended to add in some examples of boxline exclusion in Sysudoku Ba ..read more

Starting with a 2-fill, two 3-fills, and a 4-fill near collapse, there’s value by value action left in the bypass for only one value. Scroll back for the givens and trace out the bypass. An x-fill lists the values to be filled in the line. The square bracketed effects are the clues and subsets placed in the line Here’s the grid you take into box marking. Box marking adds all candidates which are members of box slinks, strong links due to having exactly two of the same value in a box. Box slinks are marked in the same position at the tops of cells. Some slinks are already marked. They are ..read more

Systematic Sudoku (Sysudoku) is a human engineered way to solve Sudoku puzzles, and provides graphic and completely documented examples and collection reviews at all levels. Diagrams and tables that aid solving are demonstrated.  Over 500 weekly posts give complete examples with move by move traces for you to follow, and detailed diagrams of highlighted moves. Actively reading traces, by filliing your own grid as you anticipate, then verify each move, is an excellent way to discover and appreciate new techniques, and new situations. The Menu Bar accesses the site elements are described be ..read more

This closing post adds two examples of a fierce looking line marking being de-fanged by hidden dublex on the over abundant X values A double line exclusion, or dublex, is one of the primary moves of Basic sudoku, in which the intersection of two parallel lines through a box cannot contain a candidate of the dublex value, forcing a third line chute to contain a true candidate of the value. When each of the intersecting lines only contain candidates of the value, then each contains a true candidate.  We just don’t know which line remainder contains which true candidate. We call that a hid ..read more

Scroll back one for the reason for the change in plans, but this is the first of several weekend puzzles from the Washington Post, added at the last minute for additional illustrations of Sysudoku Basic solving.   Basic starts with a 2-fill and moves smartly to this point. What happens on value 6? If you’re reading the trace, you only need to figure out the reason for W26. Going on, the trace continues with the effect of cause C8 being c6(129). That’s a signal that you could have seen the new 3-fill. But that means there was a 4-fill in c7 before C8. Did we miss it? No, the ..read more

I was closing down the weekly posts with a set of scroll down basic level puzzles, when I got another collection book , 3000 more “very hard to extreme “, for Adult puzzles. I did a few from the extreme section, and found them to be generally bordering on advanced level. Many Extreme Hard puzzles start with a value or two missing from the givens, and consequently, will have at least one very poorly restricted value on the line marked grid. It’s a situation calling for boxlines and X-wings to attack those over abundant candidates.  In the Guide, a boxline is explained as a feature of the ..read more

My Basic bypass starts with a resolved 4-fill. Did yours?  The final collapse begins with the value 8 scan resolving the naked pair left from the resolution of 3-fill c2[258]. In the bypass trace, you can discover when the previous 8 clues were found. That was a very productive 4-fill. Here is the collapse trace, and solution. Next week, another Kampbelmann Hard, 134, offers a 3-fill among the givens. Take it first. If it does not resolve immediately, you at least get a fill string to help later ..read more

Ever have a Sudoku fail to tie down a solution? Hard 109 of last post seems to fail to do so without a trial. Coloring, which has found many multiple solutions, defines the unique solution for this one. Starting with 4-fills, r2 has  no clue seeing two box cells.   But c2 places NW2 and leaves a 3-fill for later. Then in c6, we get a 4-fill bonus. It’s not practical to look for naked singles in every cell, but as you check a 4-fill you already have five values seeing the four cells. Does any cell have three more? Three more see r1c8, but only  5 is absent from c6. Two abs ..read more

Hard 143 starts with a stingy bypass, and requires box marking and some line marking. In the bypass, a r9 3-fill resolves  into SW8and the naked pair 36. W8 then follows, either from the 8’s dublex, or  from the West box 3-fill’s naked pair W12. The full Basic trace shows three clues in the bypass, and one in box marking. The box marking trace identifies the boxes in which box slinks, and line triplets (“t”) occur, for each value. In the box marking event NE3m, the “m”, standing for slink “marks”, is added because the slink occurs on the 6: list, rather than the 3: list. Each tra ..read more

A second Kampbelmann Hard is tough on paper, but  gives way routinely to a systematic bypass. Here is the grid well into the bypass, with a large number of cells held in reserve by box filling naked pairs. In the trace, we’re at value 9, just before r5[258] is resolved. The rest is routine follow up. Next week, the third and last Kampbelmann,  Hard 143, is harder, carrying into line marking, after giving an opportunity to show a box 3-fill (West) in the trace ..read more