TECHNIQUE 2 OF 4
A satisfied clue makes its other neighbours safe
Sometimes counting mines tells you where not to find them. Once a clue's full mine requirement is accounted for, every remaining neighbour is safe to reveal.
The rule
If a revealed number equals the count of established adjacent mines, none of its other neighbouring squares can be a mine. A revealed zero is the simplest case: all of its neighbours are safe. In the classic game, revealing a zero opens its connected empty area and bordering numbers automatically.
A common mistake
A displayed mine counter reduced by your flags does not prove those flags are correct. Local safety follows from the clue and established mine positions, not from how confidently you marked them.
TRY IT 1 · mines-all-safe-1
| C1 | C2 | C3 | C4 | C5 | C6 | |
|---|---|---|---|---|---|---|
| R1 | ||||||
| R2 | ||||||
| R3 | ||||||
| R4 | ||||||
| R5 | ||||||
| R6 |
What can you justify?
Use the a satisfied clue makes its other neighbours safe technique. What does it prove about R2C5? Treat the displayed starting marks as established facts, except flags, which the explanation must justify from revealed clues.
Written explanation
clue 0 at R1C5 still requires 0 mines among R2C5, R1C6, R2C6 after the established safe cells and proved mines are accounted for. Player flags are not used as evidence. Therefore R2C5 is safe.
TRY IT 2 · mines-all-safe-2
| C1 | C2 | C3 | C4 | C5 | C6 | |
|---|---|---|---|---|---|---|
| R1 | ||||||
| R2 | ||||||
| R3 | ||||||
| R4 | ||||||
| R5 | ||||||
| R6 |
What can you justify?
Use the a satisfied clue makes its other neighbours safe technique. What does it prove about R5C6? Treat the displayed starting marks as established facts, except flags, which the explanation must justify from revealed clues.
Written explanation
clue 0 at R6C6 still requires 0 mines among R5C6, R5C5 after the established safe cells and proved mines are accounted for. Player flags are not used as evidence. Therefore R5C6 is safe.
A player flag cannot certify its neighbours
A revealed 1 touches a flagged square A and two other hidden squares B and C. The flag at A was a guess; no further constraints about A, B or C have been established.
The tempting move
Reveal B and C as proved safe because the clue already has one flag beside it.
Why it fails
The clue counts actual mines, not flags. A could be safe while B or C contains the mine. Subtracting a guessed flag makes the safety claim conditional on an unproved assumption.
What is actually justified
The three squares contain one mine, but these facts do not identify it. Obtain evidence for A before using it in an all-safe deduction.
Transfer the idea
A revealed 2 touches two proved mines and three unresolved squares. What may you conclude about all three squares? Does this reveal which numbers will appear there?
Check your reasoning
All three squares are safe because the clue's two mines are already accounted for. Their own numbers are not determined by this fact; they can touch other mines outside the first clue's neighbourhood.