  We investigate inference of variable-length codes in other domains of
computer science, such as noisy information transmission or information
retrieval-storage: in such topics, traditionally mostly constant-length
codewords act. The study is relied upon the two concepts of independent and
closed sets. We focus to those word relations whose images are computed by
applying some peculiar combinations of deletion, insertion, or substitution. In
particular, characterizations of variable-length codes that are maximal in the
families of $\tau$-independent or $\tau$-closed codes are provided.
