anchor.diff:  
   /// A garbage-collected keyed array.
   /// TODO: once this is well-tested, let's consider moving into Prime.
  -type KeyedArray<'k, 'v when 'k : comparison> = KeyedArray.KeyedArray<'k, 'v>+type KeyedArray<'k, 'v when 'k : equality> = KeyedArray.KeyedArray<'k, 'v>
positive.code:         &karr.[key]
  
      /// Make a KeyedArray with the given compaction threshold and initial capaticy.
      let make<'k, 'v when 'k : comparison> threshold capacity : KeyedArray<'k, 'v> =
          { Keys_ = SortedDictionary<int, 'k> ()
            Indices_ = Dictionary<'k, int> ()
            Values_ = Array.zeroCreate capacity
  
negative.code: 
      /// A garbage-collected keyed array.
      /// TODO: once this is well-tested, let's consider moving into Prime.
      type [<NoEquality; NoComparison>] KeyedArray<'k, 'v when 'k : equality> =
          private
              { Keys_ : SortedDictionary<int, 'k> // sorted so that compacting does not change order
                Indices_ : Dictionary<'k, int>
  