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We provide a general framework to remove short advice by formulating the following computational task for a function f: given two oracles at least one of which is honest (i.e. correctly computes f on all inputs) as well as an input, the task is to compute f on the input with the help of the oracles by a probabilistic polynomial-time machine, which we shall call a selector. We characterize the languages for which short advice can be removed by the notion of selector: a paddable language has a selector if and only if short advice of a probabilistic machine that accepts the language can be removed under any relativized world. Previously, instance checkers have served as a useful tool to remove short advice of probabilistic computation. We indicate that existence of instance checkers is a property stronger than that of removing short advice: although no instance checker for EXP^NP-complete languages exists unless EXP^NP = NEXP, we prove that there exists a selector for any EXP^NP-complete language, by building on the proof of MIP = NEXP by Babai, Fortnow, and Lund (1991).
@InProceedings{hirahara:LIPIcs.CCC.2015.244,
author = {Hirahara, Shuichi},
title = {{Identifying an Honest EXP^NP Oracle Among Many}},
booktitle = {30th Conference on Computational Complexity (CCC 2015)},
pages = {244--263},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-81-1},
ISSN = {1868-8969},
year = {2015},
volume = {33},
editor = {Zuckerman, David},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2015.244},
URN = {urn:nbn:de:0030-drops-50718},
doi = {10.4230/LIPIcs.CCC.2015.244},
annote = {Keywords: nonuniform complexity, short advice, instance checker, interactive proof systems, probabilistic checkable proofs}
}