香农第一定理指出了平均码长与信源之间的关系，同时也指出了可以通过编码使平均码长达到极限值，这是一个很重要的极限定理。-Shannon first theorem that the average yards long with the letter of the relationship between the source, it has also pointed out the code can make the average yards long reach limits, this is a very important Limit Theorem.