anchor.diff:                      arr.[idx] <- add hkv earr (dep + 1) entry
                       Multiple arr
       
  -                | Bucket _ ->
  +                | Gutter _ ->
       
                       // logically should never hit here
                       failwithumf ()
  
positive.code:     /// A hash-key-value triple, implemented with a struct for efficiency.
      type private Hkv<'k, 'v when 'k :> IEquatable<'k>> =
          struct
              new (h, k, v) = { H = h; K = k; V = v }
              val H : int
              val K : 'k
              val V : 'v
  
negative.code: 
      /// Get the value of a property.
      let inline getPropertyValue indices (p : PropertyInfo) (x : obj) = p.GetValue (x, indices)
  
      /// Test for reference equality.
      let inline refEq (x : 'a) (y : 'a) = obj.ReferenceEquals (x, y)
  