anchor.diff:  //
   namespace ExtCore.Collections
   
  -open System.Collections
   open System.Collections.Generic
   open System.Diagnostics
   open LanguagePrimitives
  
positive.code:         | Empty -> 0
          | Lf (_,_) -> 1
          | Br (_,_,_,_) as t ->
              // TODO : Run some experiments to determine if this is a good initial capacity,
              // or if there is a more suitable value.
              let stack = System.Collections.Generic.Stack (64)
  
              // Add the initial tree to the stack.
              stack.Push t
  
negative.code:         | Br (_,_,_,_) as t ->
              let action = FSharpFunc<_,_,_>.Adapt action
  
              /// The stack of trie nodes pending traversal.
              let stack = Stack (defaultTraversalStackSize)
  
              // Add the initial tree to the stack.
              stack.Push t
  