public boolean canAppend(HistoryCell last) {
			return ((last.action == U.BasicAction.Delete && this.action == U.BasicAction.Delete && //
					((last.x1 == this.x1 || last.x1 == this.x2) && last.y1 == this.y1))//
					|| (last.action == U.BasicAction.Insert && this.action == U.BasicAction.Insert && //
							((last.x1 == this.x1 || last.x2 == this.x1) && last.y1 == this.y1)));
		}