Example 2.3.3 In digital data communications, one is interested in reliably transmitting a sequence of bits (zeros and ones) over a noisy channel.
In order to detect errors, one extra bit often is added to each block of, say, k bits.
This parity check bit is made to be a 0 or a 1 as needed so that the resulting sequence of k+1 elements has an even (or add, depending on the conventions) number of 1’s.