20dd63aabf
Fixes an issue reported on Zulip; see the test case. * Modifies the `MonadBacktrack` instance for `SimpM` to also backtrack the `UsedSimps` field. * When calling the discharger, `saveState`, and then `restoreState` if something goes wrong. I'm not certain that it makes sense to restore the `MetaM` state if discharging fails. I can easily change this to more conservatively just backtrack the `UsedSimps` after failed discharging.
19 lines
717 B
Text
19 lines
717 B
Text
-- As reported at https://leanprover.zulipchat.com/#narrow/stream/287929-mathlib4/topic/simp.3F.20giving.20nonsense.20lemmas/near/403082483
|
||
|
||
universe u
|
||
|
||
-- {α : Type} works as expected, as does specializing this lemma for `Nat`.
|
||
@[simp]
|
||
theorem tsub_eq_zero_of_le {α : Type u} [LE α] [Sub α] [OfNat α 0] {a b : α} :
|
||
a ≤ b → a - b = 0 := by sorry
|
||
|
||
@[simp]
|
||
theorem ge_iff_le (x y : Nat) : x ≥ y ↔ y ≤ x := Iff.rfl
|
||
|
||
set_option tactic.simp.trace true
|
||
|
||
-- This used to report: `Try this: simp only [ge_iff_le, Nat.succ_sub_succ_eq_sub]`
|
||
-- because we were not backtracking the "used simps" when the discharger failed.
|
||
example {n : Nat} : n = 2 - (n + 1) := by
|
||
simp [Nat.succ_sub_succ_eq_sub]
|
||
sorry
|