A simple derivation of the undetected error probabilities of complementary codes

Recently, Fu, Klove, and Wei (2003) have shown that the undetected error probability of a binary code is related to that of its complement, and the undetected error probability of a constant-weight binary code is related to that of its complement relative to the set of all constant-weight vectors. We generalize these relations to cover the complements of any binary or nonbinary code relative to a distance-invariant code containing the first code. We prove the generalization using a much simpler argument than the published proofs of the special cases.