anchor.diff:  
   let pCodeExpr = pCode >>= mkSubP
   
  -let expr = pTxt1 <|> ((+) <!> pCodeExpr <*> pTxt)
  +let expr = pword1 <|> ((+) <!> pCodeExpr <*> pword)
   
   let grammar = strJoin >> strLen64 <!> many expr
   
   // PART 2
   
  -let pStrLen  = strLen64 <!> pTxt
  -let pStr1Len = strLen64 <!> pTxt1
  +let pStrLen  = strLen64 <!> pword
  +let pStr1Len = strLen64 <!> pword1
   
   let rec mkSubPLen (x, y) =
     (fun str ->
  
positive.code: 
  // PART 1
  
  let pTxt  = charsToString <!> many letter
  let pTxt1 = charsToString <!> many1 letter
  
  let pIntPair = pint32 <* pchar 'x' <**> pint32
  
  
negative.code: open FParsec
  open FParsecOp
  
  let strJoin (xs : string list) =
    xs |> List.fold (+) ""
  let strLen64 = String.length >> int64
  