public void setc (int i, int j, int c)
	{
		synchronized (Pos)
		{
			Action a;
			if (P.color(i, j) == 0) // empty?
			{
				Node n = Pos.node();
				if (GF.getParameter("puresgf", true)
					&& (n.contains("B") || n.contains("W"))) n = newnode();
				n.addchange(new Change(i, j, 0));
				if (c > 0)
				{
					a = new Action("AB", Field.string(i, j));
				}
				else
				{
					a = new Action("AW", Field.string(i, j));
				}
				n.expandaction(a); // note the move action
				P.color(i, j, c);
				update(i, j);
			}
		}
	}