PencilPress 73 and Master Class 100

Two Basic level reviews continue with Pencil Press  bottom right, page 73 and Tom Sheldon’s Master Class 100.Two Basic level reviews continue with Pencil Press  bottom right, page 73 and Tom Sheldon’s Master Class 100.

Let’s begin with a Sysudoku survey on your ppbr 73. In your trace, did you add C6 before SW6, following the blog convention? Conventions help if you’re tracing to do comparisons.

Here is the grid after the run on 6. Do you continue with S8? Or is it (SW7, SW9)? The Sysudoku principle is to uncover all of a cause’s effects, before taking up the next cause. The next cause is the next effect on the current list, or the first effect on the next list.


The 73 trace is completed after a look at Master Class 100:


The trace looks normal, until you get into line marking and see two X-wings with no immediate effects. What is going on becomes more clear when you note that we are still in line marking, and there are possible X-wing eliminations in lines not yet marked.

X-wings are  detected as their second lines are marked. And yes, at that time, lines containing the X-wing’s eliminations may not have been marked.

That’s true of both of the X-wings spotted here.

The fish icons remain in place to “remember” the X-wing until all affected lines are marked. This technique that is not even possible in basic procedures that are detailed elsewhere, when there are any. The slink marking of Sysudoku Basic is essential to this X-wing filter in line marking. Nowhere else are there X-wing diagrams like the above.

There’s not much left to do on Master Class 100.

So how did you call it in ppbr 73? By virtue of the “cup” configuration it forms in the SW box, SW6 can be held responsible for a 79 naked pair, which 9r7c6 converts into (SW7, SW9). The bypass trace then reads:


Next post, the review of Pencil Press Extreme Sudoku  concludes with ppbr 81 at left.  The  last page with a bottom right puzzle is page 87.

The update of Tom Sheldon’s Master Class review continues with 110.

About Sudent

I'm John Welch, a retired engineering professor, father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. Sudoku analysis and illustration is a great hobby and a healthy mental challenge.
This entry was posted in Advanced Solving, Basic Solving Procedures, Puzzle Reviews, Sheldon and tagged , , , , , . Bookmark the permalink.

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