## Practical considerations

In practice, computing the G-construction using Algorithm  is only feasible for high-rate codes, because the algorithm needs to maintain a list of coset leaders at each iteration. In theory, it might be possible to use approximation techniques to store only ``important'' coset leaders, but we leave this as an open problem.

Another problem with the G-construction is that it is theoretically possible for bounding to be so severe as to halt the construction when, for example, does not return a vector for a particular code . Though we have not seen this with trellis state bounding (i.e. using the mapping ), we have seen indications that this can occur with . Of course, certain constraints will simply not correspond to any existing linear code, so this problem is inherent to code design.

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