Summary
Dijkstra has given a derivation of an efficient algorithm for a problem concerning monotonic subsequences, and extracted a proof of a related theorem from the algorithm. Here it is shown that a careful separation of concerns can lead to a beautiful conventional proof, a very different derivation of Dijkstra's algorithm, a more elegant proof from the algorithm, and the discovery of a duality property.
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References
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Pritchard, P. Another look at the “longest ascending subsequence” problem. Acta Informatica 16, 87–91 (1981). https://doi.org/10.1007/BF00289592
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DOI: https://doi.org/10.1007/BF00289592