... we choose to do so in such a manner as to minimize the average numberof questions needed. We need to be concerned with the average number to rule o ut luckyguesses identifying the sequence.might ... s e quence, i .e. , NH(X) bits. If there is noise, it will containless. We know, however, that H(X|Y ) measures the number of bits per letter neededto correct an observed Y sequence, therefore ... need to refer to facts ata different level of descr iption, one that involves the concept of knowledge. A furtherstatement is required, to the e ect that: ‘Because of these correlations, we...