public static IEnumerable<Tuple<int, int>> M(int n)
        {
            Func<int, int, int> gcp = (a, b) => 
            {
                while (b != 0)
                    b = a % (a = b);
                return a;
            };
            Func<int, int, Tuple<int, int>> f = (s1, s2) =>
                {
                    var t = gcp(s1, s2);
                    return Tuple.Create(s1 / t, s2 / t);
                };
            
            var src = Enumerable.Range(1, n);
            var res = (from s1 in src
                       from s2 in src
                       where s2 > s1
                       select f(s1, s2))
                      .Distinct();
            return res;
        }