Three numbers together
When no pair of numbers is enough, try the ways the mines can lie around three of them.
Pick three numbers that share hidden cells. Try each way the mines of the middle one could lie, and check it against the other two. The layouts that break a number are out. A cell that is a mine in every layout left, or safe in every one, is proven.
How it works
No two of these numbers prove anything here. Look at the three highlighted numbers together.
Your turn
Each board is a real position from a game. Tap or click to open; right-click, long-press or switch on Flag to place a flag. If you are not sure, take a hint: the first one only shows where to look.
Which hidden cells can you be sure of?
How the exercises were chosen
A computer checked every board: in what you see, no number and no pair of numbers proves anything; three numbers together prove exactly the marked cells.