public void Example4()
 {
     Assert.AreEqual(new List <string> {
         "aabb", "abab", "abba", "baab", "baba", "bbaa"
     },
                     Permutations.SinglePermutations2("aabb").OrderBy(x => x).ToList());
 }
 public void Example1()
 {
     Assert.AreEqual(new List <string> {
         "a"
     }, Permutations.SinglePermutations("a").OrderBy(x => x).ToList());
 }