public object[] GetAsXML()
{
return((from cell in Cells()
orderby cell.Row, cell.Col
select new XElement("cell", new XAttribute("coord", cell.Coords),
from num in cell.Numbers()
orderby num.Number
select new XElement("number", num.Number, new XAttribute("state", Converters.SudokuNumberStateToString(num.State)))
)).ToArray());
}