public void changemove (int i, int j)
	// change a move to a new field (dangerous!)
	{
		if (P.color(i, j) != 0) return;
		synchronized (Pos)
		{
			ListElement la = Pos.node().actions();
			while (la != null)
			{
				Action a = (Action)la.content();
				if (a.type().equals("B") || a.type().equals("W"))
				{
					undonode();
					a.arguments().content(Field.string(i, j));
					setnode();
					break;
				}
			}
		}
	}