This post continues the Sysudoku Basic review of Puzzleproof Extreme Sudoku 2, with reports on 70 and 91.
In the basic trace of Pzlpf2 70, there is the typical heavy bypass, and collapse in the 9: box marking list. The first box marking clue comes as the 9 value partners with the earlier 7 value for a hidden pair C79, squeeze out for C8.
Then we watch as N5 restricts N8 placement for the hidden dublex clue NEhdx8.
Trace conventions intervene shortly after, as one of the hidden dublex effects, a 3-fill in c9, can be resolved immediately, but is third on the effects list. The resolution falls instead to NE6m, the second hdx effect. All effects of NE6m are listed ahead of any effects of c9.
The conventions help trace writers compare traces, but sometimes produce surprising results.
The next Puzzleproof Extreme 2 for review is 91. An explosive collapse is triggered when 7- slinks in C and S generate the hidden dublex Nhdx7.
This time, the 3-fill r3 is immediately resolved, and the first effect NE6 places N6, and N3 as well, leaving only two N cells.
The pair N29 is resolved by given 9r7c6, and causes N2 and N9 are held in reserve as N3 generates decisive effects.
This is a primary feature of basic traces, to use effects like clues, slinks and unresolved 3-fills,
but also to hold them in reserve as causes, bringing them up after effects of earlier causes are thoroughly explored.
Next we report on Puzzleproof Extreme 2 puzzles 112 and 133.