Sysudoku weekly posts will soon be ending. This post may be the last one from the Akron Beacon Journal CREATORS series. In this one, Sysudoku box marking rescues us from a very stingy bypass, in ABJ Creators of 4/20/22.
The bypass trace, shows no 4-fills or 3-fills. The two 4-fills created by the bypass, c2[1234] and c5[2578], are not marked on the trace or the grid because they don’t resolve immediately. The spotting check: in c2, values 578 that see two fill cells are not missing. In c5, 3 and 6 are not missing, and 8 does not see a third fill cell. Value 5 sees three fill cells in 5-fills r6 and r7, one short.
Box marking is almost complete, when the 8 slink joins the 2-slink in the North box for a naked pair N28 to start a collapse.
The collapse carries to the solution,
when NW3 creates the second naked pair NE36.
Weekly posts continue with three Basic level puzzles from Hard Sudoku for Adults, by Kampbelmann , dated without copyright notice April 2020, among the toughest I tried on paper without tracing and full 3 and 4 fill analysis.
Next is Kampbelmann 50, which can be solved in Sysudoku Basic bypass.
Systematic Sudoku 