[ refactor ] Data.Fin.Properties of decidable equality, plus knock-ons
#2740
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This was referenced Jun 21, 2025
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In the absence of a review yet, I'll lift out the bug fixes as a separate PR, as per @JacquesCarette 's comment on #2743 |
JacquesCarette
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Jun 26, 2025
| @@ -110,6 +110,12 @@ m ≟ n = map′ (≡ᵇ⇒≡ m n) (≡⇒≡ᵇ m n) (T? (m ≡ᵇ n)) | |||
| ≟-diag : (eq : m ≡ n) → (m ≟ n) ≡ yes eq | |||
| ≟-diag = ≡-≟-identity _≟_ | |||
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| ≟-diag-refl : ∀ n → (n ≟ n) ≡ yes refl | |||
| ≟-diag-refl _ = ≟-diag refl | |||
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This one, on the other hand, seems to fail the Fairbairn test.
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Well, the reflexive case us what I use for Fin, and I dislike having the APIs for Nat and Fin diverging... what is really prefer would be to only have diag refer to the refl version but... legacy names!
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This PR supersedes the knock-on changes for
Permutationin #2738 and adds some new lemmas abouttransposewhich simplify the dependency graph. The contribution can be seen as a belated corollary to the changes introduced in #645 / #1732 .Downstream, we might want to revisit the dependency graph now between
Relation.Nullary.DecidableAxiom.UniquenessOfIdentityProofsRelation.Binary.PropositionalEqualityin putting these pieces together?
Outstanding (naming) issue: I followed the existing
Data.Nat.Properties.≟-diagconvention inData.Fin.Properties, and then backported thereflinstantiation of this toData.Nat.Properties.≟-diag-refl... but it occurs to me that it's hard to imagine instances of≟-diagwhich would use a general equality, and even if they were to, the use ofdiagought (?) to be a codeword for a repeated argument/reflexive equality? I just couldn't face the deprecation headache though... so a v3.0 downstreambreakingchange might be in order?