说道Redundancy，怎么定义正式呢？
The redundancy of a random event depends on how uncertain its outcome is, compared to how uncertain a variable on the same probability space could be.
注意，这里有个potential outcome思考：
The latter is defifined by the maximum entropy distribution Hmax(X) on the set of possible outcomes X.
....maximum entropy is equal to the log number of possible states.
还是看截图吧：
为什么呢？因为这种情况下，是假设均匀分布，大家都等可能，每个发生的概率是1/|X|，得到以上公式。
因此：
The redundancy W is the difffference between this maximum entropy and the actual entropy of the random variable:
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