public void Difluoroethene()
 {
     GeneratorTest.RoundTrip("F[C@H]=[C@H]F");
     GeneratorTest.RoundTrip("F[C@@H]=[C@@H]F");
     GeneratorTest.RoundTrip("F[C@H]=[C@@H]F");
     GeneratorTest.RoundTrip("F[C@@H]=[C@H]F");
 }
 public void Difluoroethene_permute()
 {
     GeneratorTest.RoundTrip("F[C@H]=[C@H]F",
                             new int[] { 1, 0, 2, 3 },
                             "[C@@H](F)=[C@H]F");
     GeneratorTest.RoundTrip("[C@@H](F)=[C@H]F",
                             new int[] { 1, 0, 2, 3 },
                             "F[C@H]=[C@H]F");
 }