OK, shame on me, I can't even do a singleton properly. I have
implemented this a thousand dozen times, but I guess I've now been
awake too long.

Here's the relevant snippet. When I compile, it rightly points out that
the member _plain, in the method GetPlain(int, int) requires an object
reference. But I cannot do a this._plain in that method too because it
is a static method.

How on earth do I get out of this circle. I bet this is a trivial thing
and I have done it countless times but just now my brain is revolting.

public class Plain: IRectangularGrid, IDisposable /*It is difficult to
spell Plateau every time, so I am naming it Plain*/
    {
        private Plain _plain = null;    /*Singleton*/

        public static Plain GetPlain(POINT upperRight)
        {
            return GetPlain(upperRight.x, upperRight.y);
        }

        public static Plain GetPlain(int upperRightX, int upperRightY)
        {
            if (_plain == null)
                _plain = new Plain(upperRightX, upperRightY);

            return _plain;
        }

        private Plain(int upperRightX, int upperRightY)
        {
                                      //some stuff
        }

My head is swirling round. Please tell me what I am missing.