Bit Strings.

• An \(n\)-bit string is a bit string of length \(n\text{.}\) That is, it is a string containing \(n\) symbols, each of which is a bit, either 0 or 1.

• The weight of a bit string is the number of 1's in it.

• \(\B^n\) is the set of all \(n\)-bit strings.

• \(\B^n_k\) is the set of all \(n\)-bit strings of weight \(k\text{.}\)