What might be the effect of moving your pawn <BD>a2-e4</BD>?
From white's perspective, this move establishes the path: c1-e5; however, it also establishes a path for black's king: g7-c3. Therefore a preemptive tactical move <BD>c1-e3</BD> will prevent black from impeding white's movement, while maintaining the path a2-e4.
