This post reaches the halfway point in the review of Manuel Castillo’s Only Extreme collection, with Only Extreme 175. A double UR, a regular Sue de Coq and irregular XYZ-wing prepare the bv field for coloring, and an XY chain coloring wrap.

A challenging Sysudoku basic,

leads to a busy, unbalanced grid.  Advanced work begins with a Type 1 unique rectangle with two removals.  Neither victim can be present if an obvious multiplicity is to be avoided.

A rare treat is the Sue de Coq hidden in the brambles, that removes seven marks and triggers a box/line removing four more.

Manuel’s Halloween treats continue with an irregular 784 -wing.  The 7 wink attaching the 47-wing is an ER 7-chain.

Also irregular is the  4r9c2 victim seeing two of the toxic 4’s by grouped 4-chain.

The X-panels are less generous, so after a quick survey of the bv field, I get out the crayons.

My usual blue/green starting cluster is surrounded by a red/orange one when it stalls.  There are two traps.

More tellingly, in this clash of clusters, it turns out that blue and orange are incompatible. Going a little further, so are blue and red.  Since we must have red or orange, blue must go.

In logical expression this computes as:

Not(blue and orange) and not(blue and red) = (green or red) and (green or orange)

                                                                                = green and (red or orange) = green

 Two wrongs don’t make a right, but these two mismatches do make a wrap.

 Looking at the revised bv map,  there is  a long XY chain with four  removals, including a red 3.     This is a wrap by XY chain, always a possibility with coloring.    Here it starts an immediate collapse.

Next time, 43 Extreme Sudoku later, it would be Only Extreme 218, but this review is interrupted for breaking news, a report on the Akron 2017 Sudoku Tournament.  Watch this space.