anchor.diff:  
       let select (db : DB.db) =
           DB.get db key
  -            |> Option.map DB.deserialize<Value>
  +            |> Option.map (DB.deserialize<IntValue> >> intvalue_to_value)
             
       let db = DB.opendb self.filename in
   
  
positive.code: type Key   = bytes * bytes
  type IntKey = cbytes * cbytes
  type Value = bytes * bool
  
  type dhdb = {
      filename: string;
  
negative.code: (* ------------------------------------------------------------------------------- *)
  let intkey_to_key (a,b) = abytes(a),abytes(b)
  let key_to_intkey (a,b) = cbytes(a),cbytes(b)
  
  (* ------------------------------------------------------------------------------- *)
  let intvalue_to_value (a,b) = abytes(a),b
  let value_to_intvalue (a,b) = cbytes(a),b
  
  (* ------------------------------------------------------------------------------- *)
  let create (filename:string) =
  