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Concretely , using the canonical trivialization of the density bundles in the presence of a metric , the Paneitz operator P can be represented in terms of a representative the Riemannian metric g as an ordinary operator on functions that transforms according under a conformal change according to the rule The operator was originally derived by working out specifically the lower-order correction terms in order to ensure conformal invariance .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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