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#1: Mark (swinbum) on Mar 23, 2012 [HINT]

When line logic fails to progress, I had to do some of what can either be described as two-way logic or guessing, depending on your point of view:

The block of 3 in row 19 can either be in columns 13-15 or 18-20. If it's in the latter then R19C13-15 must be empty, as is R18C18, and so R18C13-15 are black. That means that R17C13 and R17C15 are black, which contradicts the clue for R17. Therefore R19C15-17 are black. From there on it solves simply.

I'm not entirely comfortable with this "logic" as I consider it guesswork due to the number of steps required to force a contradiction. Can anyone else provide a simpler, more logical solution that I have missed ?

you were on the right track but look at this step in the same area: instead of supposing the 3 clue from r19 is in c18-20 (which forces the 5 clue from r18 into c13-15) just start with the assumption that the 5 clue from r18 starts in c13-15
you get the same result (violating r17 and thus getting a dot in r18c13 and then solving it out with line logic) with much less look ahead

great image by the way although he does look quite a bit more evil here than is typical (maybe it is the eyes)

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jan would but even if he doesnt gator would and he is the only other person who can mark puzzles as logically solvable or not but neither of them has been around much anymore
oh well
there are also a few other good solvers on this site (based on those who routinely share their solving talents) that i am sure would consider this logically solvable

what's funny is that i was looking in the same area and got the same dot but was looking at it a bit differently...if 5 in R18 starts in C13 then the 2-1-2 clue combo (C13,14,15) will necessarily make two "1" clues that have to go in R12 or R14, but there is only one "1" clue available.

nice image.

Generally the criterion for "moderate lookahead" is you only have to look a step or two ahead before finding a contradiction.

If you can still find it logically but it takes more than a couple of steps ahead (in other words, it can be mentally tracked without placing any dots or squares, but takes more moves to find a contradiction), it can be considered "deep lookahead."

If no one can figure out a way to figure out what goes next without either guessing or making an assumption based on the image, we call it "guessing."

The amount one has to look ahead for this puzzle definitely fits under "moderate lookahead," but as mentioned, only Jan and gator can make final decisions on that, so all we can do is help push whether or not the little question mark shows up. :)

I have been doing these puzzles for only a couple of months but had been doing Dell Logic Puzzles magazine for a long time. I have been wondering about that same issue, ie what constitutes guessing and what constitutes deep look-ahead. If I can choose an outcome and follow it through to an incorrect conclusion in few enough steps without marking the board it definitely seems like "look ahead" but if it takes many steps and I can't then see how it got to the inconsistency it seems like guessing. (Except better than the guessing where you hit "check" to see if it is right ;-) ) I was also looking at that horizontal group of 3 and the horizontal group of 5 mentioned above- I usually start with the one that does not look like it would make a good image. It seems a little like cheating or looking for a hint to consider the image.

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