anchor.diff:                                               (4, 1)
                                                (5, 1)
                                                (6, 1) ]) : Multiset<int>)
  -                 .SetName("Appending two msets works as expected") ]
  +                 .SetName("Appending two disjoint msets works as expected") ]
   
           /// <summary>
           ///     Tests <c>Multiset.append</c>.
  
positive.code:     ///     The result of appending <c>xs</c> to <c>ys</c>.
      /// </returns>
      let append xs ys =
          // TODO(CaptainHayashi): a more efficient algorithm for this.
          Seq.append (toFlatSeq xs) (toFlatSeq ys) |> ofFlatSeq
  
      /// <summary>
      ///     Maps <c>f</c> over a multiset.
  
negative.code:                  .Returns(MSet (Map.ofList [ (4, 1) ; (5, 1) ] )
                                 : Multiset<int>)
                   .SetName("Appending an empty mset and x yields x")
                (tcd [| (Multiset.ofFlatList [1; 2; 3; 4; 5] : Multiset<int>)
                        (Multiset.ofFlatList [2; 4; 4; 5; 6] : Multiset<int>) |])
                   .Returns(MSet (Map.ofList [ (1, 1)
                                               (2, 2)
                                               (3, 1)
                                               (4, 3)
                                               (5, 2)
                                               (6, 1) ]) : Multiset<int>)
                   .SetName("Appending two overlapping msets works as expected") 
                (tcd [| (Multiset.ofFlatList [1; 3; 5] : Multiset<int>)
                        (Multiset.ofFlatList [2; 4; 6] : Multiset<int>) |])
                   .Returns(MSet (Map.ofList [ (1, 1)
  