* @param shift the number of columns by which to shift
	 */
	private void shiftCol( int colNum, int shift )
	{
		Colinfo info = getColInfo( colNum );
		int oldCol = colNum;
		int newCol = oldCol + shift;

		List<BiffRec> cells;
		try
		{
			cells = getCellsByCol( colNum );
			for( BiffRec cell : cells )
			{
				cell.setCol( (short) newCol );
				updateDimensions( cell.getRowNumber(), cell.getColNumber() );
			}
		}
		catch( CellNotFoundException e )
		{
			// No cells exist in this column
		}

		if( null != info )
		{
			int first = info.getColFirst();
			if( (first == oldCol) || (first > newCol) )
			{
				info.setColFirst( newCol );
			}

			int last = info.getColLast();
			if( (last == oldCol) || (last < newCol) )
			{
				info.setColLast( newCol );
			}
		}
	}