At the edge of the casbah, Colonel Noam Tibon and his patrol funnel from their jeeps and spread out. It's 1 a.m. and the dark streets of Nablus, under curfew for almost four months, are deserted. Twelve hours ago, a Palestinian gunman shot two Israeli border policemen on this spot. Even now, the shadows and silence are deceptive. "If we stand here a few more minutes, they'll shoot at us," says Tibon, the 40-year-old commander of the Nahal Brigade. In those circumstances, most people would leave right away. But Tibon plans to stay.