The decoder must have the same probability estimation the encoder used, which can either be sent in advance, derived from already transferred data or be part of the compressor and decompressor.

• 解码器必须与编码器有同样的概率估计，这种概率估计可以事先发送过去、从已经发送的数据导出或者作为压缩器或者解压器的一部分。