[Merged by Bors] - feat: demote the instance Fintype.ofIsEmpty to a def #8816
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Mathlib/Data/Fintype/Card.lean
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| /-- Note: this lemma is specifically about `Fintype.of_is_empty`. For a statement about | ||
| arbitrary `Fintype` instances, use `Fintype.card_eq_zero_iff`. -/ | ||
| @[simp] | ||
| theorem card_of_isEmpty [IsEmpty α] : Fintype.card α = 0 := | ||
| rfl | ||
| #align fintype.card_of_is_empty Fintype.card_of_isEmpty |
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We should keep this lemma, but stated using a letI := Fintype.ofIsEmpty
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It is a particular case of card_eq_zero, so why keep it?
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Because this one works with dsimp
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ok, I've added it back.
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Thanks! 🎉 |
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Rationale: this instance creates (empty) data out of nothing, which may conflict with other data. If you have in the context `[Fintype i]` and case on whether `i` is empty or not, then this gave two non-defeq instances of `[Fintype i]` around.
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Rationale: this instance creates (empty) data out of nothing, which may conflict with other data. If you have in the context `[Fintype i]` and case on whether `i` is empty or not, then this gave two non-defeq instances of `[Fintype i]` around.
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Pull request successfully merged into master. Build succeeded: |
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Rationale: this instance creates (empty) data out of nothing, which may conflict with other data. If you have in the context `[Fintype i]` and case on whether `i` is empty or not, then this gave two non-defeq instances of `[Fintype i]` around.
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Rationale: this instance creates (empty) data out of nothing, which may conflict with other data. If you have in the context
[Fintype i]and case on whetheriis empty or not, then this gave two non-defeq instances of[Fintype i]around.