Naturality of join_assoc and trijoin_twist #1783
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Alizter
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Oct 14, 2023
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Alizter
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I've had a quick look and looks good to me.
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This proves that
trijoin_twistis natural. Combined with the naturality ofjoin_sym, this gives the naturality ofjoin_assoc. Direct proofs seemed hard, but by phrasing things using a newfunctor_trijoindefined usingtrijoin_recit was possible to make this fairly clean, using naturality oftrijoin_recandtrijoinrecdata_fun_twist. Along the way, I removed rarely used arguments tois1natural_natequivandis1natural_nattrans, and addedisnat_natequiv, which is needed because another ambiguous coercion doesn't work.