Sorry, I think my comment was confusing, you're absolutely on the right track! To get an idea of how close you are: For 5-4, one of your two answers is right. 1-C's uniqueness doesn't rely on "shade some cells", though that's indeed a rule. 3-C indeed needs green on that ?. All of these are based on just the 3 big rules. edit: I think you've pretty much understood the implicit rules?