public void ThreeTest()
        {
            var four  = SparseByWeight.Dec(Five);
            var three = SparseByWeight.Dec(four);

            Assert.AreEqual("2,1", DumpNat(Three));
            Assert.AreEqual("2,1", DumpNat(three));
        }
        public void FourTest()
        {
            var four = SparseByWeight.Dec(Five);

            Assert.AreEqual("4", DumpNat(four));
        }