  A malleable coding scheme considers not only compression efficiency but also
the ease of alteration, thus encouraging some form of recycling of an old
compressed version in the formation of a new one. Malleability cost is the
difficulty of synchronizing compressed versions, and malleable codes are of
particular interest when representing information and modifying the
representation are both expensive. We examine the trade-off between compression
efficiency and malleability cost under a malleability metric defined with
respect to a string edit distance. This problem introduces a metric topology to
the compressed domain. We characterize the achievable rates and malleability as
the solution of a subgraph isomorphism problem. This can be used to argue that
allowing conditional entropy of the edited message given the original message
to grow linearly with block length creates an exponential increase in code
length.
