16 lines
645 B
Text
16 lines
645 B
Text
-- As reported at https://leanprover.zulipchat.com/#narrow/stream/287929-mathlib4/topic/simp.3F.20giving.20nonsense.20lemmas/near/403082483
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universe u
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-- {α : Type} works as expected, as does specializing this lemma for `Nat`.
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@[simp]
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theorem tsub_eq_zero_of_le {α : Type u} [LE α] [Sub α] [OfNat α 0] {a b : α} :
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a ≤ b → a - b = 0 := by sorry
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set_option tactic.simp.trace true
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-- This used to report: `Try this: simp only [ge_iff_le, Nat.succ_sub_succ_eq_sub]`
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-- because we were not backtracking the "used simps" when the discharger failed.
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example {n : Nat} : n = 2 - (n + 1) := by
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simp [Nat.succ_sub_succ_eq_sub]
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sorry
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