What is a unique-solution puzzle
A unique-solution puzzle has exactly one right finish. Every empty cell has one value that works with the rules. If two finishes both looked legal, the puzzle would be broken.
On DIGIGMA every live puzzle is unique: Sudoku, Star Battle, and Binary Puzzle. That is why you can eliminate. If a digit, a star, or a 0 would leave no legal finish, it is wrong — you do not need to try it and see.
You do not need to guess. Forced moves come from the rules and from uniqueness together. When you are stuck, look for a cell that has only one legal place left.
How-tos: Sudoku, Star Battle, Binary Puzzle. Or Play from the home page.