Thanks, had some enjoyable Thanks, had some enjoyable time solving them. I think the defining feature of these puzzles is that you cannot be totally sure that you have solved them! Disagreements about what constitutes a solution are entirely possible (just like for an ethical problem for example). I am not even sure how to prove that a solution like "objects that are exactly like the ones on the left go to the left and all others go to the right" is bogus. So yes, seems like a pretty good example of what you call "nebulosity".