Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bio-inspired Synthetic Ivory as a Sustainable Material for Piano Keys   Natural ivory is no longer readily or legally available, as it is obtained
primarily from elephant tusks, which now enjoy international protection. Ivory,
however, is the best material known for piano keys. We present a
hydroxylapatite-gelatin biocomposite that is chemically identical to natural
ivory but with functional properties optimized to replace it. As this
biocomposite is fabricated from abundant materials in an environmentally
friendly process and is furthermore biodegradable, it is a sustainable solution
for piano keys with the ideal functional properties of natural ivory.

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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg