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 values 4, 6 and 7 were all present in c7 before C8 made it a 3-fill. Resolving 3-fill c6(129, 1 and 9 in r6 places C2, leaving the naked pair 19 to be resolved by N1 and a naked pair 35 in r5.
The bypass finishes on value 9, with np67 adding a np35, and a 3-fill in r5 resolving into three bv.
If you’re reading the traces, notice how the box 3-fill 
and the bv refill (r5) are marked. In the box marking trace, the naked pair SW45 leaves a 3-fill, resolved to a clue and pair. SW1m is marking a strong link on 1. The link is marked by “m” inside the trace of a different value, 5. Next in this trace, 6 and 9 in r1 force the 3-fill r8[369] and NE7.
Now we’re ready for line marking. It requires care to avoid using candidates covered by unmarked lines. It helps to designate bv where they are really defined.
The collapse on the second line is quick,
but building the cluster to a wrap of blue is even easier.
For next week, we’ll throw in Kampelmann Hard 109 that turned out to be much worse than hard. See if you get far enough to see what I mean.
Systematic Sudoku 