LINQ Demo

static void Main(string[] args)
        {
            var points = new List<Point>();
            points.Add(new Point
            {
                X = 1,
                Y = 2
            });
            points.Add(new Point
            {
                X = 0.5,
                Y = -0.25
            });
            points.Add(new Point
            {
                X = 0.5,
                Y = 0.5
            });
            points.Add(new Point
            {
                X = -1,
                Y = -2
            });

            var points1 =
                from Point pt in points
                where ((pt.X * pt.X) + (pt.Y * pt.Y)) <=1
                orderby pt.Y descending
                select pt;

            foreach (var item in points1)
            {
                Console.WriteLine("{0} {1}",item.X, item.Y);
            }