The last Sudoku of Dave Green’s Labor Day Weekend, the Sunday 5-Star, has a challenging sysudokie bypass and line marking, barely staying within the lines of basic solving. Even on a ©PowerPoint grid, this puzzle would be a nightmare with number scanned candidates.

Action begins in the NW box, as a crosshatched NW1 allows aligned givens 3,5 => NWnp35,  leaving NW2 and 2 cells for NWnp89, and a 2f: r2np46.

Then unwritten

SE7m => E7, and the

Ec8 wall => E5m => SE5.

In 3f: c8, 4,6 will force NEnp46 and hidden single 8.

The dublex SW9 leaves a resolvable 3f: in r8.

To finish up the bypass, 2 and 4 are box/lined, into a naked pair in r8, then

7&9 in SW, r6 and c3 =>Wnp79. 

Then E5m&W5m => E5.

Next comes an easy box marking and very tough line marking, showing how the Bradley Hand ITC font holds up with long fill strings. 

We’re rescued from advanced solving by a 6f: naked triple.

Here is the entire trace. You don’t want to miss a naked triple like this one.

The Dave Green puzzles of this Labor Day Weekend series bring out the stimulating challenge of the slink marking bypass, and basic level Sudoku puzzles. Next week we start a review of Denis Berthier’s 2007 book, The Hidden Logic of Sudoku, looking for human solving insights.  You might want to dig out or pull up your copy.