This is one of the most fundamental strategies available for the solving of Minesweeper puzzles. If you make a puzzle having a difficulty
level of 1, then you will be able to solve it completely using only this strategy plus the
Required Mine strategy.
The five cells highlighted in blue draw your attention to the hazard cell containing a 1. This cell requires a single adjacent mine, and
reference to cell C3-R4 shows that this requirement has already been met. As no further mines are required, the highlighted cells may all be
cleared.