static class EnumerableExtensions
    {
        public static double Max(this IEnumerable<double> source)
        {
            using (var en = source.GetEnumerator())
            {
                if (!en.MoveNext())
                    throw new ArgumentException("empty seq");
                var currmax = en.Current;
                while (en.MoveNext())
                    if (en.Current > currmax)
                        currmax = en.Current;
                return currmax;
            }
        }
    }