Step 5 of 5

Flag or Reveal

Flag what’s proved, open what’s proved, and nothing else.

The rule of thumb: Every move is proved: flag only certain mines, open only certain safe cells, and chord a number once its flags are right.

Every move is a claim: “this is a mine” or “this is safe.” Make only the ones a number proves. A hunch is a guess, and every board here is solvable without guessing.

A wrong flag is worse than no flag. The numbers around it look finished when they aren’t, a chord on them opens a mine, and the mine counter lies to you in the endgame.

Once a number touches all its flags, click it to chord: the game opens its other hidden neighbors at once. A practice here counts only if you clear it without ever flagging a safe cell. Hints are fine: they only place proved flags.

Where to look: Before each flag, name the number that proves it. Before each chord, check that every flag around the number was proved.

Worked example

A real position from a 9×9 board with 12 mines. Purple: the numbers the reasoning rests on. Dashed: the cells in question. Green: what it proves. Red: a flag placed on a hunch, and the mine it costs you.

Proved: The 1 at row 3, column 6 needs 1 more mine and has one hidden cell left touching it, so that cell is a mine. Flag it (green).

Now the 1 at row 1, column 6 touches its flag. Click it to chord: its other hidden neighbor opens (green), every one proved safe.

Rewind, and suppose you had flagged row 1, column 7 on a hunch instead (red dashes). The 1 looks finished, so a chord opens row 2, column 7: a mine (red). One unproved flag loses the board.

Practice it ↓