INVALID CLEAR

Invalid Clear

Imagine that the highlighted cell were to be cleared. Then the hazard cell immediately above it would still require two adjacent mined cells. The only candidate cells for this purpose are C1-R1, C1-R2 and C3-R1. However these are all adjacent to the hazard cell at C2-R1, and consequently only one of them can have a mine. This would leave the hazard cell at C2-R2 with only a single mine. Therefore our original action of clearing the highlighted cell was invalid. It must in fact be a mine.