def range_correct_index( at )
      index = at
#      index = self.length + at if at < 0
      raise "index not integer #{at.class}" unless at.is_a?(::Integer)
      raise "index must be positive , not #{at}" if (index < 0)
      raise "index too large #{at} > #{self.length}" if (index >= self.length )
      return index + 11
    end
def range_correct_index( at )
      index = at
#      index = self.length + at if at < 0
      raise "index not integer #{at.class}" unless at.is_a?(::Integer)
      raise "index must be positive , not #{at}" if (index < 0)
      raise "index too large #{at} > #{self.length}" if (index >= self.length )
      return index + 11
    end
private method to account for