We study the problem of finding a Tarski fixed point over the k-dimensional grid [n]^k. We give a black-box reduction from the Tarski problem to the same problem with an additional promise that the input function has a unique fixed point. It implies that the Tarski problem and the unique Tarski problem have exactly the same query complexity. Our reduction is based on a novel notion of partial-information functions which we use to fool algorithms for the unique Tarski problem as if they were working on a monotone function with a unique fixed point.
@InProceedings{chen_et_al:LIPIcs.CCC.2023.21, author = {Chen, Xi and Li, Yuhao and Yannakakis, Mihalis}, title = {{Reducing Tarski to Unique Tarski (In the Black-Box Model)}}, booktitle = {38th Computational Complexity Conference (CCC 2023)}, pages = {21:1--21:23}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-282-2}, ISSN = {1868-8969}, year = {2023}, volume = {264}, editor = {Ta-Shma, Amnon}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2023.21}, URN = {urn:nbn:de:0030-drops-182919}, doi = {10.4230/LIPIcs.CCC.2023.21}, annote = {Keywords: Tarski fixed point, Query complexity, TFNP} }
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