anchor.diff:                                  traverse (path.AppendBit false) l
                                   traverse (path.AppendBit true) r
   
  -                    traverse (Codeword(0uy, 0us)) tree
  +                    traverse Codeword.Empty tree
                       arr  
   
   
  
positive.code:                 let v = uint16 (off + v)
                  let huff = coder.dcChromaInv.[dc]
                  x.Write(huff)
                  x.Write(Codeword(byte dc, v))
  
              member x.WriteACChrom(leadingZeros : int, v : int) =
                  assert(leadingZeros < 16) 
  
negative.code:                 let v = uint16 (off + v)
                  let huff = coder.dcLumInv.[dc]
                  x.Write(huff)
                  x.Write(Codeword.Create(dc, v))
  
              member x.WriteACLum(leadingZeros : int, v : int) =
                  assert(leadingZeros < 16) 
  