diff --git a/Std/Data/List/Lemmas.lean b/Std/Data/List/Lemmas.lean index 54044dd03b..1a5aa9a726 100644 --- a/Std/Data/List/Lemmas.lean +++ b/Std/Data/List/Lemmas.lean @@ -1055,6 +1055,9 @@ theorem all_eq_not_any_not (l : List α) (p : α → Bool) : l.all p = !l.any (! @[simp] theorem mem_reverse {x : α} {as : List α} : x ∈ reverse as ↔ x ∈ as := by simp [reverse] +@[simp] theorem reverse_eq_nil_iff {xs : List α} : xs.reverse = [] ↔ xs = [] := by + induction xs <;> simp + /-! ### insert -/ section insert