Rytter (1986) proves that the complementary problem, of testing for the existence of a string with two decodings, is NL-complete, and therefore that unique decipherability is co-NL-complete. The equivalence of NL-completeness and co-NL-completeness follows from the Immerman–Szelepcsényi theorem. Rytter, Wojciech (1986). "The space complexity of the unique decipherability problem". Information Processing Letters. 23 (1): 1–3. doi:10.1016/0020-0190(86)90121-3. MR0853618..
doi.org
Rodeh (1982). Rodeh, M. (1982). "A fast test for unique decipherability based on suffix trees (Corresp.)". IEEE Transactions on Information Theory. 28 (4): 648–651. doi:10.1109/TIT.1982.1056535..
Rytter (1986) proves that the complementary problem, of testing for the existence of a string with two decodings, is NL-complete, and therefore that unique decipherability is co-NL-complete. The equivalence of NL-completeness and co-NL-completeness follows from the Immerman–Szelepcsényi theorem. Rytter, Wojciech (1986). "The space complexity of the unique decipherability problem". Information Processing Letters. 23 (1): 1–3. doi:10.1016/0020-0190(86)90121-3. MR0853618..