From cade9753218c5a53627861a492f76a692f61863b Mon Sep 17 00:00:00 2001
From: Kim Morrison <kim@tqft.net>
Date: Thu, 14 Nov 2024 10:23:11 +1100
Subject: [PATCH] chore: adaptations for nightly-2024-11-12 (#1040)

Co-authored-by: leanprover-community-mathlib4-bot <leanprover-community-mathlib4-bot@users.noreply.github.com>
Co-authored-by: Mario Carneiro <di.gama@gmail.com>
---
 Batteries/Data/Array/Basic.lean      |   8 +-
 Batteries/Data/Array/Lemmas.lean     |  48 ----------
 Batteries/Data/Array/Merge.lean      |   2 +-
 Batteries/Data/Array/Monadic.lean    |   2 +-
 Batteries/Data/Array/OfFn.lean       |   4 -
 Batteries/Data/Array/Pairwise.lean   |   2 +-
 Batteries/Data/BinaryHeap.lean       |   2 +-
 Batteries/Data/ByteArray.lean        |   8 +-
 Batteries/Data/Fin/Basic.lean        |  54 -----------
 Batteries/Data/Fin/Lemmas.lean       | 128 ---------------------------
 Batteries/Data/HashMap/Basic.lean    |   7 +-
 Batteries/Data/List/Basic.lean       |  32 -------
 Batteries/Data/List/OfFn.lean        |  34 -------
 Batteries/Data/MLList/Basic.lean     |   2 +-
 Batteries/Data/String/Lemmas.lean    |   2 +-
 Batteries/Data/UnionFind/Basic.lean  | 128 +++++++++++++--------------
 Batteries/Data/UnionFind/Lemmas.lean |   2 +-
 Batteries/Data/Vector/Basic.lean     |   2 +-
 BatteriesTest/array.lean             |   2 +-
 lean-toolchain                       |   2 +-
 20 files changed, 83 insertions(+), 388 deletions(-)

diff --git a/Batteries/Data/Array/Basic.lean b/Batteries/Data/Array/Basic.lean
index 403c42d9e2..8be0bc967d 100644
--- a/Batteries/Data/Array/Basic.lean
+++ b/Batteries/Data/Array/Basic.lean
@@ -46,7 +46,7 @@ considered.
 protected def minD [ord : Ord α]
     (xs : Array α) (d : α) (start := 0) (stop := xs.size) : α :=
   if h: start < xs.size ∧ start < stop then
-    xs.minWith (xs.get ⟨start, h.left⟩) (start + 1) stop
+    xs.minWith xs[start] (start + 1) stop
   else
     d
 
@@ -60,7 +60,7 @@ considered.
 protected def min? [ord : Ord α]
     (xs : Array α) (start := 0) (stop := xs.size) : Option α :=
   if h : start < xs.size ∧ start < stop then
-    some $ xs.minD (xs.get ⟨start, h.left⟩) start stop
+    some $ xs.minD xs[start] start stop
   else
     none
 
@@ -135,7 +135,7 @@ A proof by `get_elem_tactic` is provided as a default argument for `h`.
 This will perform the update destructively provided that `a` has a reference count of 1 when called.
 -/
 abbrev setN (a : Array α) (i : Nat) (x : α) (h : i < a.size := by get_elem_tactic) : Array α :=
-  a.set ⟨i, h⟩ x
+  a.set i x
 
 /--
 `swapN a i j hi hj` swaps two `Nat` indexed entries in an `Array α`.
@@ -201,7 +201,7 @@ subarray, or `none` if the subarray is empty.
 def popHead? (as : Subarray α) : Option (α × Subarray α) :=
   if h : as.start < as.stop
     then
-      let head := as.array.get ⟨as.start, Nat.lt_of_lt_of_le h as.stop_le_array_size⟩
+      let head := as.array[as.start]'(Nat.lt_of_lt_of_le h as.stop_le_array_size)
       let tail :=
         { as with
           start := as.start + 1
diff --git a/Batteries/Data/Array/Lemmas.lean b/Batteries/Data/Array/Lemmas.lean
index 8a5544089d..daf0493b88 100644
--- a/Batteries/Data/Array/Lemmas.lean
+++ b/Batteries/Data/Array/Lemmas.lean
@@ -22,48 +22,6 @@ theorem forIn_eq_forIn_toList [Monad m]
 
 /-! ### zipWith / zip -/
 
-theorem toList_zipWith (f : α → β → γ) (as : Array α) (bs : Array β) :
-    (as.zipWith bs f).toList = as.toList.zipWith f bs.toList := by
-  let rec loop : ∀ (i : Nat) cs, i ≤ as.size → i ≤ bs.size →
-      (zipWithAux f as bs i cs).toList =
-        cs.toList ++ (as.toList.drop i).zipWith f (bs.toList.drop i) := by
-    intro i cs hia hib
-    unfold zipWithAux
-    by_cases h : i = as.size ∨ i = bs.size
-    case pos =>
-      have : ¬(i < as.size) ∨ ¬(i < bs.size) := by
-        cases h <;> simp_all only [Nat.not_lt, Nat.le_refl, true_or, or_true]
-      -- Cleaned up aesop output below
-      simp_all only [Nat.not_lt]
-      cases h <;> [(cases this); (cases this)]
-      · simp_all only [Nat.le_refl, Nat.lt_irrefl, dite_false, List.drop_length,
-                      List.zipWith_nil_left, List.append_nil]
-      · simp_all only [Nat.le_refl, Nat.lt_irrefl, dite_false, List.drop_length,
-                      List.zipWith_nil_left, List.append_nil]
-      · simp_all only [Nat.le_refl, Nat.lt_irrefl, dite_false, List.drop_length,
-                      List.zipWith_nil_right, List.append_nil]
-        split <;> simp_all only [Nat.not_lt]
-      · simp_all only [Nat.le_refl, Nat.lt_irrefl, dite_false, List.drop_length,
-                      List.zipWith_nil_right, List.append_nil]
-        split <;> simp_all only [Nat.not_lt]
-    case neg =>
-      rw [not_or] at h
-      have has : i < as.size := Nat.lt_of_le_of_ne hia h.1
-      have hbs : i < bs.size := Nat.lt_of_le_of_ne hib h.2
-      simp only [has, hbs, dite_true]
-      rw [loop (i+1) _ has hbs, Array.push_toList]
-      have h₁ : [f as[i] bs[i]] = List.zipWith f [as[i]] [bs[i]] := rfl
-      let i_as : Fin as.toList.length := ⟨i, has⟩
-      let i_bs : Fin bs.toList.length := ⟨i, hbs⟩
-      rw [h₁, List.append_assoc]
-      congr
-      rw [← List.zipWith_append (h := by simp), getElem_eq_getElem_toList,
-        getElem_eq_getElem_toList]
-      show List.zipWith f (as.toList[i_as] :: List.drop (i_as + 1) as.toList)
-        ((List.get bs.toList i_bs) :: List.drop (i_bs + 1) bs.toList) =
-        List.zipWith f (List.drop i as.toList) (List.drop i bs.toList)
-      simp only [length_toList, Fin.getElem_fin, List.getElem_cons_drop, List.get_eq_getElem]
-  simp [zipWith, loop 0 #[] (by simp) (by simp)]
 @[deprecated (since := "2024-09-09")] alias data_zipWith := toList_zipWith
 @[deprecated (since := "2024-08-13")] alias zipWith_eq_zipWith_data := data_zipWith
 
@@ -71,12 +29,6 @@ theorem toList_zipWith (f : α → β → γ) (as : Array α) (bs : Array β) :
     (as.zipWith bs f).size = min as.size bs.size := by
   rw [size_eq_length_toList, toList_zipWith, List.length_zipWith]
 
-theorem toList_zip (as : Array α) (bs : Array β) :
-    (as.zip bs).toList = as.toList.zip bs.toList :=
-  toList_zipWith Prod.mk as bs
-@[deprecated (since := "2024-09-09")] alias data_zip := toList_zip
-@[deprecated (since := "2024-08-13")] alias zip_eq_zip_data := data_zip
-
 @[simp] theorem size_zip (as : Array α) (bs : Array β) :
     (as.zip bs).size = min as.size bs.size :=
   as.size_zipWith bs Prod.mk
diff --git a/Batteries/Data/Array/Merge.lean b/Batteries/Data/Array/Merge.lean
index 4b806a35d6..252f7a6364 100644
--- a/Batteries/Data/Array/Merge.lean
+++ b/Batteries/Data/Array/Merge.lean
@@ -94,7 +94,7 @@ set_option linter.unusedVariables.funArgs false in
 `f ⋯ (f (f x₁ x₂) x₃) ⋯ xₙ`.
 -/
 def mergeAdjacentDups [eq : BEq α] (f : α → α → α) (xs : Array α) : Array α :=
-  if h : 0 < xs.size then go (mkEmpty xs.size) 1 (xs.get ⟨0, h⟩) else xs
+  if h : 0 < xs.size then go (mkEmpty xs.size) 1 xs[0] else xs
 where
   /-- Auxiliary definition for `mergeAdjacentDups`. -/
   go (acc : Array α) (i : Nat) (hd : α) :=
diff --git a/Batteries/Data/Array/Monadic.lean b/Batteries/Data/Array/Monadic.lean
index 934111e131..ba297a9f70 100644
--- a/Batteries/Data/Array/Monadic.lean
+++ b/Batteries/Data/Array/Monadic.lean
@@ -153,7 +153,7 @@ theorem SatisfiesM_mapIdxM [Monad m] [LawfulMonad m] (as : Array α) (f : Nat 
     (hs : ∀ i, motive i.1 → SatisfiesM (p i · ∧ motive (i + 1)) (f i as[i])) :
     SatisfiesM
       (fun arr => motive as.size ∧ ∃ eq : arr.size = as.size, ∀ i h, p ⟨i, h⟩ arr[i])
-      (Array.mapIdxM as f) :=
+      (as.mapIdxM f) :=
   SatisfiesM_mapFinIdxM as (fun i => f i) motive h0 p hs
 
 theorem size_modifyM [Monad m] [LawfulMonad m] (a : Array α) (i : Nat) (f : α → m α) :
diff --git a/Batteries/Data/Array/OfFn.lean b/Batteries/Data/Array/OfFn.lean
index e02be7cba1..5233fd1f96 100644
--- a/Batteries/Data/Array/OfFn.lean
+++ b/Batteries/Data/Array/OfFn.lean
@@ -11,8 +11,4 @@ namespace Array
 
 /-! ### ofFn -/
 
-@[simp]
-theorem toList_ofFn (f : Fin n → α) : (ofFn f).toList = List.ofFn f := by
-  apply ext_getElem <;> simp
-
 end Array
diff --git a/Batteries/Data/Array/Pairwise.lean b/Batteries/Data/Array/Pairwise.lean
index 82ace9609f..498c070540 100644
--- a/Batteries/Data/Array/Pairwise.lean
+++ b/Batteries/Data/Array/Pairwise.lean
@@ -20,7 +20,7 @@ that `as` is strictly sorted and `as.Pairwise (· ≤ ·)` asserts that `as` is
 def Pairwise (R : α → α → Prop) (as : Array α) : Prop := as.toList.Pairwise R
 
 theorem pairwise_iff_get {as : Array α} : as.Pairwise R ↔
-    ∀ (i j : Fin as.size), i < j → R (as.get i) (as.get j) := by
+    ∀ (i j : Fin as.size), i < j → R (as.get i i.2) (as.get j j.2) := by
   unfold Pairwise; simp [List.pairwise_iff_get, getElem_fin_eq_getElem_toList]
 
 theorem pairwise_iff_getElem {as : Array α} : as.Pairwise R ↔
diff --git a/Batteries/Data/BinaryHeap.lean b/Batteries/Data/BinaryHeap.lean
index 29a273a9d0..897cca1c2a 100644
--- a/Batteries/Data/BinaryHeap.lean
+++ b/Batteries/Data/BinaryHeap.lean
@@ -88,7 +88,7 @@ def size (self : BinaryHeap α lt) : Nat := self.1.size
 def vector (self : BinaryHeap α lt) : Vector α self.size := ⟨self.1, rfl⟩
 
 /-- `O(1)`. Get an element in the heap by index. -/
-def get (self : BinaryHeap α lt) (i : Fin self.size) : α := self.1.get i
+def get (self : BinaryHeap α lt) (i : Fin self.size) : α := self.1[i]'(i.2)
 
 /-- `O(log n)`. Insert an element into a `BinaryHeap`, preserving the max-heap property. -/
 def insert (self : BinaryHeap α lt) (x : α) : BinaryHeap α lt where
diff --git a/Batteries/Data/ByteArray.lean b/Batteries/Data/ByteArray.lean
index 6a95a241aa..86a495e2df 100644
--- a/Batteries/Data/ByteArray.lean
+++ b/Batteries/Data/ByteArray.lean
@@ -15,7 +15,7 @@ theorem getElem_eq_data_getElem (a : ByteArray) (h : i < a.size) : a[i] = a.data
 /-! ### uget/uset -/
 
 @[simp] theorem uset_eq_set (a : ByteArray) {i : USize} (h : i.toNat < a.size) (v : UInt8) :
-    a.uset i v h = a.set ⟨i.toNat, h⟩ v := rfl
+    a.uset i v h = a.set i.toNat v := rfl
 
 /-! ### empty -/
 
@@ -45,7 +45,7 @@ theorem get_push_lt (a : ByteArray) (x : UInt8) (i : Nat) (h : i < a.size) :
 /-! ### set -/
 
 @[simp] theorem data_set (a : ByteArray) (i : Fin a.size) (v : UInt8) :
-    (a.set i v).data = a.data.set i v := rfl
+    (a.set i v).data = a.data.set i v i.isLt := rfl
 @[deprecated (since := "2024-08-13")] alias set_data := data_set
 
 @[simp] theorem size_set (a : ByteArray) (i : Fin a.size) (v : UInt8) :
@@ -60,7 +60,7 @@ theorem get_set_ne (a : ByteArray) (i : Fin a.size) (v : UInt8) (hj : j < a.size
   Array.get_set_ne (h:=h) ..
 
 theorem set_set (a : ByteArray) (i : Fin a.size) (v v' : UInt8) :
-    (a.set i v).set ⟨i, by simp [i.2]⟩ v' = a.set i v' :=
+    (a.set i v).set i v' = a.set i v' :=
   ByteArray.ext <| Array.set_set ..
 
 /-! ### copySlice -/
@@ -132,7 +132,7 @@ def ofFn (f : Fin n → UInt8) : ByteArray where
   simp [get, Fin.cast]
 
 @[simp] theorem getElem_ofFn (f : Fin n → UInt8) (i) (h : i < (ofFn f).size) :
-    (ofFn f)[i] = f ⟨i, size_ofFn f ▸ h⟩ := get_ofFn ..
+    (ofFn f)[i] = f ⟨i, size_ofFn f ▸ h⟩ := get_ofFn f ⟨i, h⟩
 
 private def ofFnAux (f : Fin n → UInt8) : ByteArray := go 0 (mkEmpty n) where
   go (i : Nat) (acc : ByteArray) : ByteArray :=
diff --git a/Batteries/Data/Fin/Basic.lean b/Batteries/Data/Fin/Basic.lean
index b61481e33a..346f3006e5 100644
--- a/Batteries/Data/Fin/Basic.lean
+++ b/Batteries/Data/Fin/Basic.lean
@@ -14,57 +14,3 @@ def enum (n) : Array (Fin n) := Array.ofFn id
 
 /-- `list n` is the list of all elements of `Fin n` in order -/
 def list (n) : List (Fin n) := (enum n).toList
-
-/--
-Folds a monadic function over `Fin n` from left to right:
-```
-Fin.foldlM n f x₀ = do
-  let x₁ ← f x₀ 0
-  let x₂ ← f x₁ 1
-  ...
-  let xₙ ← f xₙ₋₁ (n-1)
-  pure xₙ
-```
--/
-@[inline] def foldlM [Monad m] (n) (f : α → Fin n → m α) (init : α) : m α := loop init 0 where
-  /--
-  Inner loop for `Fin.foldlM`.
-  ```
-  Fin.foldlM.loop n f xᵢ i = do
-    let xᵢ₊₁ ← f xᵢ i
-    ...
-    let xₙ ← f xₙ₋₁ (n-1)
-    pure xₙ
-  ```
-  -/
-  loop (x : α) (i : Nat) : m α := do
-    if h : i < n then f x ⟨i, h⟩ >>= (loop · (i+1)) else pure x
-  termination_by n - i
-
-/--
-Folds a monadic function over `Fin n` from right to left:
-```
-Fin.foldrM n f xₙ = do
-  let xₙ₋₁ ← f (n-1) xₙ
-  let xₙ₋₂ ← f (n-2) xₙ₋₁
-  ...
-  let x₀ ← f 0 x₁
-  pure x₀
-```
--/
-@[inline] def foldrM [Monad m] (n) (f : Fin n → α → m α) (init : α) : m α :=
-  loop ⟨n, Nat.le_refl n⟩ init where
-  /--
-  Inner loop for `Fin.foldrM`.
-  ```
-  Fin.foldrM.loop n f i xᵢ = do
-    let xᵢ₋₁ ← f (i-1) xᵢ
-    ...
-    let x₁ ← f 1 x₂
-    let x₀ ← f 0 x₁
-    pure x₀
-  ```
-  -/
-  loop : {i // i ≤ n} → α → m α
-  | ⟨0, _⟩, x => pure x
-  | ⟨i+1, h⟩, x => f ⟨i, h⟩ x >>= loop ⟨i, Nat.le_of_lt h⟩
diff --git a/Batteries/Data/Fin/Lemmas.lean b/Batteries/Data/Fin/Lemmas.lean
index 5010e1310f..d799e2e6f3 100644
--- a/Batteries/Data/Fin/Lemmas.lean
+++ b/Batteries/Data/Fin/Lemmas.lean
@@ -56,32 +56,6 @@ theorem list_reverse (n) : (list n).reverse = (list n).map rev := by
 
 /-! ### foldlM -/
 
-theorem foldlM_loop_lt [Monad m] (f : α → Fin n → m α) (x) (h : i < n) :
-    foldlM.loop n f x i = f x ⟨i, h⟩ >>= (foldlM.loop n f . (i+1)) := by
-  rw [foldlM.loop, dif_pos h]
-
-theorem foldlM_loop_eq [Monad m] (f : α → Fin n → m α) (x) : foldlM.loop n f x n = pure x := by
-  rw [foldlM.loop, dif_neg (Nat.lt_irrefl _)]
-
-theorem foldlM_loop [Monad m] (f : α → Fin (n+1) → m α) (x) (h : i < n+1) :
-    foldlM.loop (n+1) f x i = f x ⟨i, h⟩ >>= (foldlM.loop n (fun x j => f x j.succ) . i) := by
-  if h' : i < n then
-    rw [foldlM_loop_lt _ _ h]
-    congr; funext
-    rw [foldlM_loop_lt _ _ h', foldlM_loop]; rfl
-  else
-    cases Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.not_lt.1 h')
-    rw [foldlM_loop_lt]
-    congr; funext
-    rw [foldlM_loop_eq, foldlM_loop_eq]
-termination_by n - i
-
-@[simp] theorem foldlM_zero [Monad m] (f : α → Fin 0 → m α) (x) : foldlM 0 f x = pure x :=
-  foldlM_loop_eq ..
-
-theorem foldlM_succ [Monad m] (f : α → Fin (n+1) → m α) (x) :
-    foldlM (n+1) f x = f x 0 >>= foldlM n (fun x j => f x j.succ) := foldlM_loop ..
-
 theorem foldlM_eq_foldlM_list [Monad m] (f : α → Fin n → m α) (x) :
     foldlM n f x = (list n).foldlM f x := by
   induction n generalizing x with
@@ -93,32 +67,6 @@ theorem foldlM_eq_foldlM_list [Monad m] (f : α → Fin n → m α) (x) :
 
 /-! ### foldrM -/
 
-theorem foldrM_loop_zero [Monad m] (f : Fin n → α → m α) (x) :
-    foldrM.loop n f ⟨0, Nat.zero_le _⟩ x = pure x := by
-  rw [foldrM.loop]
-
-theorem foldrM_loop_succ [Monad m] (f : Fin n → α → m α) (x) (h : i < n) :
-    foldrM.loop n f ⟨i+1, h⟩ x = f ⟨i, h⟩ x >>= foldrM.loop n f ⟨i, Nat.le_of_lt h⟩ := by
-  rw [foldrM.loop]
-
-theorem foldrM_loop [Monad m] [LawfulMonad m] (f : Fin (n+1) → α → m α) (x) (h : i+1 ≤ n+1) :
-    foldrM.loop (n+1) f ⟨i+1, h⟩ x =
-      foldrM.loop n (fun j => f j.succ) ⟨i, Nat.le_of_succ_le_succ h⟩ x >>= f 0 := by
-  induction i generalizing x with
-  | zero =>
-    rw [foldrM_loop_zero, foldrM_loop_succ, pure_bind]
-    conv => rhs; rw [←bind_pure (f 0 x)]
-    congr; funext; exact foldrM_loop_zero ..
-  | succ i ih =>
-    rw [foldrM_loop_succ, foldrM_loop_succ, bind_assoc]
-    congr; funext; exact ih ..
-
-@[simp] theorem foldrM_zero [Monad m] (f : Fin 0 → α → m α) (x) : foldrM 0 f x = pure x :=
-  foldrM_loop_zero ..
-
-theorem foldrM_succ [Monad m] [LawfulMonad m] (f : Fin (n+1) → α → m α) (x) :
-    foldrM (n+1) f x = foldrM n (fun i => f i.succ) x >>= f 0 := foldrM_loop ..
-
 theorem foldrM_eq_foldrM_list [Monad m] [LawfulMonad m] (f : Fin n → α → m α) (x) :
     foldrM n f x = (list n).foldrM f x := by
   induction n with
@@ -127,41 +75,6 @@ theorem foldrM_eq_foldrM_list [Monad m] [LawfulMonad m] (f : Fin n → α → m
 
 /-! ### foldl -/
 
-theorem foldl_loop_lt (f : α → Fin n → α) (x) (h : i < n) :
-    foldl.loop n f x i = foldl.loop n f (f x ⟨i, h⟩) (i+1) := by
-  rw [foldl.loop, dif_pos h]
-
-theorem foldl_loop_eq (f : α → Fin n → α) (x) : foldl.loop n f x n = x := by
-  rw [foldl.loop, dif_neg (Nat.lt_irrefl _)]
-
-theorem foldl_loop (f : α → Fin (n+1) → α) (x) (h : i < n+1) :
-    foldl.loop (n+1) f x i = foldl.loop n (fun x j => f x j.succ) (f x ⟨i, h⟩) i := by
-  if h' : i < n then
-    rw [foldl_loop_lt _ _ h]
-    rw [foldl_loop_lt _ _ h', foldl_loop]; rfl
-  else
-    cases Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.not_lt.1 h')
-    rw [foldl_loop_lt]
-    rw [foldl_loop_eq, foldl_loop_eq]
-
-@[simp] theorem foldl_zero (f : α → Fin 0 → α) (x) : foldl 0 f x = x :=
-  foldl_loop_eq ..
-
-theorem foldl_succ (f : α → Fin (n+1) → α) (x) :
-    foldl (n+1) f x = foldl n (fun x i => f x i.succ) (f x 0) :=
-  foldl_loop ..
-
-theorem foldl_succ_last (f : α → Fin (n+1) → α) (x) :
-    foldl (n+1) f x = f (foldl n (f · ·.castSucc) x) (last n) := by
-  rw [foldl_succ]
-  induction n generalizing x with
-  | zero => simp [foldl_succ, Fin.last]
-  | succ n ih => rw [foldl_succ, ih (f · ·.succ), foldl_succ]; simp [succ_castSucc]
-
-theorem foldl_eq_foldlM (f : α → Fin n → α) (x) :
-    foldl n f x = foldlM (m:=Id) n f x := by
-  induction n generalizing x <;> simp [foldl_succ, foldlM_succ, *]
-
 theorem foldl_eq_foldl_list (f : α → Fin n → α) (x) : foldl n f x = (list n).foldl f x := by
   induction n generalizing x with
   | zero => rw [foldl_zero, list_zero, List.foldl_nil]
@@ -169,48 +82,7 @@ theorem foldl_eq_foldl_list (f : α → Fin n → α) (x) : foldl n f x = (list
 
 /-! ### foldr -/
 
-theorem foldr_loop_zero (f : Fin n → α → α) (x) :
-    foldr.loop n f ⟨0, Nat.zero_le _⟩ x = x := by
-  rw [foldr.loop]
-
-theorem foldr_loop_succ (f : Fin n → α → α) (x) (h : i < n) :
-    foldr.loop n f ⟨i+1, h⟩ x = foldr.loop n f ⟨i, Nat.le_of_lt h⟩ (f ⟨i, h⟩ x) := by
-  rw [foldr.loop]
-
-theorem foldr_loop (f : Fin (n+1) → α → α) (x) (h : i+1 ≤ n+1) :
-    foldr.loop (n+1) f ⟨i+1, h⟩ x =
-      f 0 (foldr.loop n (fun j => f j.succ) ⟨i, Nat.le_of_succ_le_succ h⟩ x) := by
-  induction i generalizing x <;> simp [foldr_loop_zero, foldr_loop_succ, *]
-
-@[simp] theorem foldr_zero (f : Fin 0 → α → α) (x) : foldr 0 f x = x :=
-  foldr_loop_zero ..
-
-theorem foldr_succ (f : Fin (n+1) → α → α) (x) :
-    foldr (n+1) f x = f 0 (foldr n (fun i => f i.succ) x) := foldr_loop ..
-
-theorem foldr_succ_last (f : Fin (n+1) → α → α) (x) :
-    foldr (n+1) f x = foldr n (f ·.castSucc) (f (last n) x) := by
-  induction n generalizing x with
-  | zero => simp [foldr_succ, Fin.last]
-  | succ n ih => rw [foldr_succ, ih (f ·.succ), foldr_succ]; simp [succ_castSucc]
-
-theorem foldr_eq_foldrM (f : Fin n → α → α) (x) :
-    foldr n f x = foldrM (m:=Id) n f x := by
-  induction n <;> simp [foldr_succ, foldrM_succ, *]
-
 theorem foldr_eq_foldr_list (f : Fin n → α → α) (x) : foldr n f x = (list n).foldr f x := by
   induction n with
   | zero => rw [foldr_zero, list_zero, List.foldr_nil]
   | succ n ih => rw [foldr_succ, ih, list_succ, List.foldr_cons, List.foldr_map]
-
-theorem foldl_rev (f : Fin n → α → α) (x) :
-    foldl n (fun x i => f i.rev x) x = foldr n f x := by
-  induction n generalizing x with
-  | zero => simp
-  | succ n ih => rw [foldl_succ, foldr_succ_last, ← ih]; simp [rev_succ]
-
-theorem foldr_rev (f : α → Fin n → α) (x) :
-     foldr n (fun i x => f x i.rev) x = foldl n f x := by
-  induction n generalizing x with
-  | zero => simp
-  | succ n ih => rw [foldl_succ_last, foldr_succ, ← ih]; simp [rev_succ]
diff --git a/Batteries/Data/HashMap/Basic.lean b/Batteries/Data/HashMap/Basic.lean
index 3fd1d3350d..a8a93dd197 100644
--- a/Batteries/Data/HashMap/Basic.lean
+++ b/Batteries/Data/HashMap/Basic.lean
@@ -40,7 +40,7 @@ Note: this is marked `noncomputable` because it is only intended for specificati
 noncomputable def size (data : Buckets α β) : Nat := (data.1.toList.map (·.toList.length)).sum
 
 @[simp] theorem update_size (self : Buckets α β) (i d h) :
-    (self.update i d h).1.size = self.1.size := Array.size_uset ..
+    (self.update i d h).1.size = self.1.size := Array.size_uset _ _ _ h
 
 /-- Map a function over the values in the map. -/
 @[specialize] def mapVal (f : α → β → γ) (self : Buckets α β) : Buckets α γ :=
@@ -143,11 +143,10 @@ where
   destroying `source` in the process. -/
   go (i : Nat) (source : Array (AssocList α β)) (target : Buckets α β) : Buckets α β :=
     if h : i < source.size then
-      let idx : Fin source.size := ⟨i, h⟩
-      let es := source.get idx
+      let es := source[i]
       -- We remove `es` from `source` to make sure we can reuse its memory cells
       -- when performing es.foldl
-      let source := source.set idx .nil
+      let source := source.set i .nil
       let target := es.foldl reinsertAux target
       go (i+1) source target
     else target
diff --git a/Batteries/Data/List/Basic.lean b/Batteries/Data/List/Basic.lean
index 3e2460f18c..77adfc783b 100644
--- a/Batteries/Data/List/Basic.lean
+++ b/Batteries/Data/List/Basic.lean
@@ -163,32 +163,8 @@ Split a list at every occurrence of a separator element. The separators are not
   | [x], acc => acc.toListAppend [f x]
   | x :: xs, acc => go xs (acc.push x)
 
-/--
-`insertIdx n a l` inserts `a` into the list `l` after the first `n` elements of `l`
-```
-insertIdx 2 1 [1, 2, 3, 4] = [1, 2, 1, 3, 4]
-```
--/
-def insertIdx (n : Nat) (a : α) : List α → List α :=
-  modifyTailIdx (cons a) n
-
 @[deprecated (since := "2024-10-21")] alias insertNth := insertIdx
 
-/-- Tail-recursive version of `insertIdx`. -/
-@[inline] def insertIdxTR (n : Nat) (a : α) (l : List α) : List α := go n l #[] where
-  /-- Auxiliary for `insertIdxTR`: `insertIdxTR.go a n l acc = acc.toList ++ insertIdx n a l`. -/
-  go : Nat → List α → Array α → List α
-  | 0, l, acc => acc.toListAppend (a :: l)
-  | _, [], acc => acc.toList
-  | n+1, a :: l, acc => go n l (acc.push a)
-
-theorem insertIdxTR_go_eq : ∀ n l, insertIdxTR.go a n l acc = acc.toList ++ insertIdx n a l
-  | 0, l | _+1, [] => by simp [insertIdxTR.go, insertIdx]
-  | n+1, a :: l => by simp [insertIdxTR.go, insertIdx, insertIdxTR_go_eq n l]
-
-@[csimp] theorem insertIdx_eq_insertIdxTR : @insertIdx = @insertIdxTR := by
-  funext α f n l; simp [insertIdxTR, insertIdxTR_go_eq]
-
 theorem headD_eq_head? (l) (a : α) : headD l a = (head? l).getD a := by cases l <;> rfl
 
 /--
@@ -548,14 +524,6 @@ def sigmaTR {σ : α → Type _} (l₁ : List α) (l₂ : ∀ a, List (σ a)) :
   rw [Array.foldl_toList_eq_flatMap]; rfl
   intros; apply Array.foldl_toList_eq_map
 
-/--
-`ofFn f` with `f : fin n → α` returns the list whose ith element is `f i`
-```
-ofFn f = [f 0, f 1, ... , f (n - 1)]
-```
--/
-def ofFn {n} (f : Fin n → α) : List α := Fin.foldr n (f · :: ·) []
-
 /-- `ofFnNthVal f i` returns `some (f i)` if `i < n` and `none` otherwise. -/
 def ofFnNthVal {n} (f : Fin n → α) (i : Nat) : Option α :=
   if h : i < n then some (f ⟨i, h⟩) else none
diff --git a/Batteries/Data/List/OfFn.lean b/Batteries/Data/List/OfFn.lean
index 93214cc99b..c66846e61a 100644
--- a/Batteries/Data/List/OfFn.lean
+++ b/Batteries/Data/List/OfFn.lean
@@ -12,38 +12,4 @@ import Batteries.Data.Fin.Lemmas
 
 namespace List
 
-@[simp]
-theorem length_ofFn (f : Fin n → α) : (ofFn f).length = n := by
-  simp only [ofFn]
-  induction n with
-  | zero => simp
-  | succ n ih => simp [Fin.foldr_succ, ih]
-
-@[simp]
-protected theorem getElem_ofFn (f : Fin n → α) (i : Nat) (h : i < (ofFn f).length) :
-    (ofFn f)[i] = f ⟨i, by simp_all⟩ := by
-  simp only [ofFn]
-  induction n generalizing i with
-  | zero => simp at h
-  | succ n ih =>
-    match i with
-    | 0 => simp [Fin.foldr_succ]
-    | i+1 =>
-      simp only [Fin.foldr_succ]
-      apply ih
-      simp_all
-
-@[simp]
-protected theorem getElem?_ofFn (f : Fin n → α) (i) : (ofFn f)[i]? = ofFnNthVal f i :=
-  if h : i < (ofFn f).length
-  then by
-    rw [getElem?_eq_getElem h, List.getElem_ofFn]
-    · simp only [length_ofFn] at h; simp [ofFnNthVal, h]
-  else by
-    rw [ofFnNthVal, dif_neg] <;>
-    simpa using h
-
-@[simp] theorem toArray_ofFn (f : Fin n → α) : (ofFn f).toArray = Array.ofFn f := by
-  ext <;> simp
-
 end List
diff --git a/Batteries/Data/MLList/Basic.lean b/Batteries/Data/MLList/Basic.lean
index 8f58c11fb8..5de23f0b53 100644
--- a/Batteries/Data/MLList/Basic.lean
+++ b/Batteries/Data/MLList/Basic.lean
@@ -334,7 +334,7 @@ partial def fin (n : Nat) : MLList m (Fin n) := go 0 where
 partial def ofArray {α : Type} (L : Array α) : MLList m α := go 0 where
   /-- Implementation of `MLList.ofArray`. -/
   go (i : Nat) : MLList m α :=
-    if h : i < L.size then cons (L.get ⟨i, h⟩) (thunk fun _ => go (i+1)) else nil
+    if h : i < L.size then cons L[i] (thunk fun _ => go (i+1)) else nil
 
 /-- Group the elements of a lazy list into chunks of a given size.
 If the lazy list is finite, the last chunk may be smaller (possibly even length 0). -/
diff --git a/Batteries/Data/String/Lemmas.lean b/Batteries/Data/String/Lemmas.lean
index 431591ebc1..642029cdd1 100644
--- a/Batteries/Data/String/Lemmas.lean
+++ b/Batteries/Data/String/Lemmas.lean
@@ -573,7 +573,7 @@ theorem extract (h₁ : ValidFor l (m ++ r) it₁) (h₂ : ValidFor (m.reverse +
     it₁.extract it₂ = ⟨m⟩ := by
   cases h₁.out; cases h₂.out
   simp only [Iterator.extract, List.reverseAux_eq, List.reverse_append, List.reverse_reverse,
-    List.append_assoc, ne_eq, not_true_eq_false, decide_False, utf8Len_append, utf8Len_reverse,
+    List.append_assoc, ne_eq, not_true_eq_false, decide_false, utf8Len_append, utf8Len_reverse,
     gt_iff_lt, pos_lt_eq, Nat.not_lt.2 (Nat.le_add_left ..), Bool.or_self, Bool.false_eq_true,
     ↓reduceIte]
   simpa [Nat.add_comm] using extract_of_valid l.reverse m r
diff --git a/Batteries/Data/UnionFind/Basic.lean b/Batteries/Data/UnionFind/Basic.lean
index c48bb5bda1..a607dc2284 100644
--- a/Batteries/Data/UnionFind/Basic.lean
+++ b/Batteries/Data/UnionFind/Basic.lean
@@ -25,39 +25,35 @@ namespace UnionFind
 
 /-- Parent of a union-find node, defaults to self when the node is a root -/
 def parentD (arr : Array UFNode) (i : Nat) : Nat :=
-  if h : i < arr.size then (arr.get ⟨i, h⟩).parent else i
+  if h : i < arr.size then arr[i].parent else i
 
 /-- Rank of a union-find node, defaults to 0 when the node is a root -/
 def rankD (arr : Array UFNode) (i : Nat) : Nat :=
-  if h : i < arr.size then (arr.get ⟨i, h⟩).rank else 0
+  if h : i < arr.size then arr[i].rank else 0
 
-theorem parentD_eq {arr : Array UFNode} {i} : parentD arr i.1 = (arr.get i).parent := dif_pos _
+theorem parentD_eq {arr : Array UFNode} {i} (h) :
+    parentD arr i = arr[i].parent := dif_pos _
 
-theorem parentD_eq' {arr : Array UFNode} {i} (h) :
-    parentD arr i = (arr.get ⟨i, h⟩).parent := dif_pos _
-
-theorem rankD_eq {arr : Array UFNode} {i} : rankD arr i.1 = (arr.get i).rank := dif_pos _
-
-theorem rankD_eq' {arr : Array UFNode} {i} (h) : rankD arr i = (arr.get ⟨i, h⟩).rank := dif_pos _
+theorem rankD_eq {arr : Array UFNode} {i} (h) : rankD arr i = arr[i].rank := dif_pos _
 
 theorem parentD_of_not_lt : ¬i < arr.size → parentD arr i = i := (dif_neg ·)
 
 theorem lt_of_parentD : parentD arr i ≠ i → i < arr.size :=
   Decidable.not_imp_comm.1 parentD_of_not_lt
 
-theorem parentD_set {arr : Array UFNode} {x v i} :
-    parentD (arr.set x v) i = if x.1 = i then v.parent else parentD arr i := by
+theorem parentD_set {arr : Array UFNode} {x v i h} :
+    parentD (arr.set x v h) i = if x = i then v.parent else parentD arr i := by
   rw [parentD]; simp only [Array.size_set, Array.get_eq_getElem, parentD]
   split
   · split <;> simp_all
-  · split <;> [(subst i; cases ‹¬_› x.2); rfl]
+  · split <;> [(subst i; cases ‹¬_› h); rfl]
 
-theorem rankD_set {arr : Array UFNode} {x v i} :
-    rankD (arr.set x v) i = if x.1 = i then v.rank else rankD arr i := by
+theorem rankD_set {arr : Array UFNode} {x v i h} :
+    rankD (arr.set x v h) i = if x = i then v.rank else rankD arr i := by
   rw [rankD]; simp only [Array.size_set, Array.get_eq_getElem, rankD]
   split
   · split <;> simp_all
-  · split <;> [(subst i; cases ‹¬_› x.2); rfl]
+  · split <;> [(subst i; cases ‹¬_› h); rfl]
 
 end UnionFind
 
@@ -126,9 +122,8 @@ instance : EmptyCollection UnionFind := ⟨.empty⟩
 /-- Parent of union-find node -/
 abbrev parent (self : UnionFind) (i : Nat) : Nat := parentD self.arr i
 
-theorem parent'_lt (self : UnionFind) (i : Fin self.size) :
-    (self.arr.get i).parent < self.size := by
-  simp only [← parentD_eq, parentD_lt, Fin.is_lt, Array.length_toList]
+theorem parent'_lt (self : UnionFind) (i : Nat) (h) : self.arr[i].parent < self.size := by
+  simp [← parentD_eq, parentD_lt, Fin.is_lt, Array.length_toList, h]
 
 theorem parent_lt (self : UnionFind) (i : Nat) : self.parent i < self.size ↔ i < self.size := by
   simp only [parentD]; split <;> simp only [*, parent'_lt]
@@ -139,20 +134,19 @@ abbrev rank (self : UnionFind) (i : Nat) : Nat := rankD self.arr i
 theorem rank_lt {self : UnionFind} {i : Nat} : self.parent i ≠ i →
     self.rank i < self.rank (self.parent i) := by simpa only [rank] using self.rankD_lt
 
-theorem rank'_lt (self : UnionFind) (i : Fin self.size) : (self.arr.get i).parent ≠ i →
-    self.rank i < self.rank (self.arr.get i).parent := by
+theorem rank'_lt (self : UnionFind) (i h) : self.arr[i].parent ≠ i →
+    self.rank i < self.rank (self.arr[i]).parent := by
   simpa only [← parentD_eq] using self.rankD_lt
 
 /-- Maximum rank of nodes in a union-find structure -/
 noncomputable def rankMax (self : UnionFind) := self.arr.foldr (max ·.rank) 0 + 1
 
-theorem rank'_lt_rankMax (self : UnionFind) (i : Fin self.size) :
-    (self.arr.get i).rank < self.rankMax := by
+theorem rank'_lt_rankMax (self : UnionFind) (i : Nat) (h) : (self.arr[i]).rank < self.rankMax := by
   let rec go : ∀ {l} {x : UFNode}, x ∈ l → x.rank ≤ List.foldr (max ·.rank) 0 l
     | a::l, _, List.Mem.head _ => by dsimp; apply Nat.le_max_left
     | a::l, _, .tail _ h => by dsimp; exact Nat.le_trans (go h) (Nat.le_max_right ..)
   simp only [Array.get_eq_getElem, rankMax, Array.foldr_eq_foldr_toList]
-  exact Nat.lt_succ.2 <| go (self.arr.toList.get_mem i.1 i.2)
+  exact Nat.lt_succ.2 <| go (self.arr.toList.get_mem i h)
 
 theorem rankD_lt_rankMax (self : UnionFind) (i : Nat) :
     rankD self.arr i < self.rankMax := by
@@ -175,17 +169,17 @@ def push (self : UnionFind) : UnionFind where
   arr := self.arr.push ⟨self.arr.size, 0⟩
   parentD_lt {i} := by
     simp only [Array.size_push, push_parentD]; simp only [parentD, Array.get_eq_getElem]
-    split <;> [exact fun _ => Nat.lt_succ_of_lt (self.parent'_lt _); exact id]
+    split <;> [exact fun _ => Nat.lt_succ_of_lt (self.parent'_lt ..); exact id]
   rankD_lt := by simp only [push_parentD, ne_eq, push_rankD]; exact self.rank_lt
 
 /-- Root of a union-find node. -/
 def root (self : UnionFind) (x : Fin self.size) : Fin self.size :=
-  let y := (self.arr.get x).parent
+  let y := self.arr[x.1].parent
   if h : y = x then
     x
   else
-    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ h)
-    self.root ⟨y, self.parent'_lt x⟩
+    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ h)
+    self.root ⟨y, self.parent'_lt x _⟩
 termination_by self.rankMax - self.rank x
 
 @[inherit_doc root]
@@ -202,9 +196,9 @@ def rootD (self : UnionFind) (x : Nat) : Nat :=
 
 @[nolint unusedHavesSuffices]
 theorem parent_root (self : UnionFind) (x : Fin self.size) :
-    (self.arr.get (self.root x)).parent = self.root x := by
+    (self.arr[(self.root x).1]).parent = self.root x := by
   rw [root]; split <;> [assumption; skip]
-  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
+  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
   apply parent_root
 termination_by self.rankMax - self.rank x
 
@@ -231,7 +225,7 @@ theorem rootD_lt {self : UnionFind} {x : Nat} : self.rootD x < self.size ↔ x <
 @[nolint unusedHavesSuffices]
 theorem rootD_eq_self {self : UnionFind} {x : Nat} : self.rootD x = x ↔ self.parent x = x := by
   refine ⟨fun h => by rw [← h, parent_rootD], fun h => ?_⟩
-  rw [rootD]; split <;> [rw [root, dif_pos (by rwa [parent, parentD_eq' ‹_›] at h)]; rfl]
+  rw [rootD]; split <;> [rw [root, dif_pos (by rwa [parent, parentD_eq ‹_›] at h)]; rfl]
 
 theorem rootD_rootD {self : UnionFind} {x : Nat} : self.rootD (self.rootD x) = self.rootD x :=
   rootD_eq_self.2 (parent_rootD ..)
@@ -271,12 +265,12 @@ structure FindAux (n : Nat) where
 
 /-- Auxiliary function for find operation -/
 def findAux (self : UnionFind) (x : Fin self.size) : FindAux self.size :=
-  let y := (self.arr.get x).parent
+  let y := self.arr[x.1].parent
   if h : y = x then
     ⟨self.arr, x, rfl⟩
   else
-    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ h)
-    let ⟨arr₁, root, H⟩ := self.findAux ⟨y, self.parent'_lt x⟩
+    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ h)
+    let ⟨arr₁, root, H⟩ := self.findAux ⟨y, self.parent'_lt _ x.2⟩
     ⟨arr₁.modify x fun s => { s with parent := root }, root, by simp [H]⟩
 termination_by self.rankMax - self.rank x
 
@@ -286,16 +280,16 @@ theorem findAux_root {self : UnionFind} {x : Fin self.size} :
   rw [findAux, root]
   simp only [Array.length_toList, Array.get_eq_getElem, dite_eq_ite]
   split <;> simp only
-  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
+  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
   exact findAux_root
 termination_by self.rankMax - self.rank x
 
 @[nolint unusedHavesSuffices]
 theorem findAux_s {self : UnionFind} {x : Fin self.size} :
-    (findAux self x).s = if (self.arr.get x).parent = x then self.arr else
-      (self.findAux ⟨_, self.parent'_lt x⟩).s.modify x fun s =>
+    (findAux self x).s = if self.arr[x.1].parent = x then self.arr else
+      (self.findAux ⟨_, self.parent'_lt x x.2⟩).s.modify x fun s =>
         { s with parent := self.rootD x } := by
-  rw [show self.rootD _ = (self.findAux ⟨_, self.parent'_lt x⟩).root from _]
+  rw [show self.rootD _ = (self.findAux ⟨_, self.parent'_lt x x.2⟩).root from _]
   · rw [findAux]; split <;> rfl
   · rw [← rootD_parent, parent, parentD_eq]
     simp only [rootD, Array.get_eq_getElem, Array.length_toList, findAux_root]
@@ -307,10 +301,11 @@ theorem rankD_findAux {self : UnionFind} {x : Fin self.size} :
     rankD (findAux self x).s i = self.rank i := by
   if h : i < self.size then
     rw [findAux_s]; split <;> [rfl; skip]
-    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
+    have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
     have := lt_of_parentD (by rwa [parentD_eq])
-    rw [rankD_eq' (by simp [FindAux.size_eq, h]), Array.get_modify]
-    split <;> simp [← rankD_eq, rankD_findAux (x := ⟨_, self.parent'_lt x⟩), -Array.get_eq_getElem]
+    rw [rankD_eq (by simp [FindAux.size_eq, h]), Array.getElem_modify]
+    split <;>
+      simp [← rankD_eq, rankD_findAux (x := ⟨_, self.parent'_lt _ x.2⟩), -Array.get_eq_getElem]
   else
     simp only [rankD, Array.data_length, Array.get_eq_getElem, rank]
     rw [dif_neg (by rwa [FindAux.size_eq]), dif_neg h]
@@ -319,13 +314,13 @@ termination_by self.rankMax - self.rank x
 set_option linter.deprecated false in
 theorem parentD_findAux {self : UnionFind} {x : Fin self.size} :
     parentD (findAux self x).s i =
-    if i = x then self.rootD x else parentD (self.findAux ⟨_, self.parent'_lt x⟩).s i := by
+    if i = x then self.rootD x else parentD (self.findAux ⟨_, self.parent'_lt _ x.2⟩).s i := by
   rw [findAux_s]; split <;> [split; skip]
   · subst i; rw [rootD_eq_self.2 _] <;> simp [parentD_eq, *, -Array.get_eq_getElem]
   · rw [findAux_s]; simp [*, -Array.get_eq_getElem]
   · next h =>
     rw [parentD]; split <;> rename_i h'
-    · rw [Array.get_modify (by simpa using h')]
+    · rw [Array.getElem_modify (by simpa using h')]
       simp only [Array.data_length, @eq_comm _ i]
       split <;> simp [← parentD_eq, -Array.get_eq_getElem]
     · rw [if_neg (mt (by rintro rfl; simp [FindAux.size_eq]) h')]
@@ -334,47 +329,48 @@ theorem parentD_findAux {self : UnionFind} {x : Fin self.size} :
 theorem parentD_findAux_rootD {self : UnionFind} {x : Fin self.size} :
     parentD (findAux self x).s (self.rootD x) = self.rootD x := by
   rw [parentD_findAux]; split <;> [rfl; rename_i h]
-  rw [rootD_eq_self, parent, parentD_eq] at h
-  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
-  rw [← rootD_parent, parent, parentD_eq]
-  exact parentD_findAux_rootD (x := ⟨_, self.parent'_lt x⟩)
+  rw [rootD_eq_self, parent, parentD_eq x.2] at h
+  have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
+  rw [← rootD_parent, parent, parentD_eq x.2]
+  exact parentD_findAux_rootD (x := ⟨_, self.parent'_lt _ x.2⟩)
 termination_by self.rankMax - self.rank x
 
 theorem parentD_findAux_lt {self : UnionFind} {x : Fin self.size} (h : i < self.size) :
     parentD (findAux self x).s i < self.size := by
-  if h' : (self.arr.get x).parent = x then
+  if h' : self.arr[x.1].parent = x then
     rw [findAux_s, if_pos h']; apply self.parentD_lt h
   else
     rw [parentD_findAux]
     split
     · simp [rootD_lt]
-    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
+    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
       apply parentD_findAux_lt h
 termination_by self.rankMax - self.rank x
 
 theorem parentD_findAux_or (self : UnionFind) (x : Fin self.size) (i) :
     parentD (findAux self x).s i = self.rootD i ∧ self.rootD i = self.rootD x ∨
     parentD (findAux self x).s i = self.parent i := by
-  if h' : (self.arr.get x).parent = x then
+  if h' : self.arr[x.1].parent = x then
     rw [findAux_s, if_pos h']; exact .inr rfl
   else
     rw [parentD_findAux]
     split
     · simp [*]
-    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
-      exact (parentD_findAux_or self ⟨_, self.parent'_lt x⟩ i).imp_left <| .imp_right fun h => by
-        simp only [h, ← parentD_eq, rootD_parent, Array.length_toList]
+    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
+      refine (parentD_findAux_or self ⟨_, self.parent'_lt _ x.2⟩ i)
+        |>.imp_left (.imp_right fun h => ?_)
+      simp only [h, ← parentD_eq, rootD_parent, Array.length_toList]
 termination_by self.rankMax - self.rank x
 
 theorem lt_rankD_findAux {self : UnionFind} {x : Fin self.size} :
     parentD (findAux self x).s i ≠ i →
     self.rank i < self.rank (parentD (findAux self x).s i) := by
-  if h' : (self.arr.get x).parent = x then
+  if h' : self.arr[x.1].parent = x then
     rw [findAux_s, if_pos h']; apply self.rank_lt
   else
     rw [parentD_findAux]; split <;> rename_i h <;> intro h'
     · subst i; rwa [lt_rank_root, Ne, ← rootD_eq_self]
-    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ ‹_›)
+    · have := Nat.sub_lt_sub_left (self.lt_rankMax x) (self.rank'_lt _ _ ‹_›)
       apply lt_rankD_findAux h'
 termination_by self.rankMax - self.rank x
 
@@ -447,46 +443,46 @@ def linkAux (self : Array UFNode) (x y : Fin self.size) : Array UFNode :=
   if x.1 = y then
     self
   else
-    let nx := self.get x
-    let ny := self.get y
+    let nx := self[x.1]
+    let ny := self[y.1]
     if ny.rank < nx.rank then
       self.set y {ny with parent := x}
     else
       let arr₁ := self.set x {nx with parent := y}
       if nx.rank = ny.rank then
-        arr₁.set ⟨y, by simp [arr₁]⟩ {ny with rank := ny.rank + 1}
+        arr₁.set y {ny with rank := ny.rank + 1} (by simp [arr₁])
       else
         arr₁
 
 theorem setParentBump_rankD_lt {arr : Array UFNode} {x y : Fin arr.size}
-    (hroot : (arr.get x).rank < (arr.get y).rank ∨ (arr.get y).parent = y)
-    (H : (arr.get x).rank ≤ (arr.get y).rank) {i : Nat}
+    (hroot : arr[x.1].rank < arr[y.1].rank ∨ arr[y.1].parent = y)
+    (H : arr[x.1].rank ≤ arr[y.1].rank) {i : Nat}
     (rankD_lt : parentD arr i ≠ i → rankD arr i < rankD arr (parentD arr i))
     (hP : parentD arr' i = if x.1 = i then y.1 else parentD arr i)
     (hR : ∀ {i}, rankD arr' i =
-      if y.1 = i ∧ (arr.get x).rank = (arr.get y).rank then
-        (arr.get y).rank + 1
+      if y.1 = i ∧ arr[x.1].rank = arr[y.1].rank then
+        arr[y.1].rank + 1
       else rankD arr i) :
     ¬parentD arr' i = i → rankD arr' i < rankD arr' (parentD arr' i) := by
   simp [hP, hR, -Array.get_eq_getElem] at *; split <;> rename_i h₁ <;> [simp [← h₁]; skip] <;>
     split <;> rename_i h₂ <;> intro h
   · simp [h₂] at h
-  · simp only [rankD_eq, Array.get_eq_getElem]
+  · simp only [rankD_eq, x.2, y.2, Array.get_eq_getElem]
     split <;> rename_i h₃
     · rw [← h₃]; apply Nat.lt_succ_self
     · exact Nat.lt_of_le_of_ne H h₃
   · cases h₂.1
     simp only [h₂.2, false_or, Nat.lt_irrefl] at hroot
-    simp only [hroot, parentD_eq, not_true_eq_false] at h
+    simp only [hroot, parentD_eq y.2, not_true_eq_false] at h
   · have := rankD_lt h
     split <;> rename_i h₃
     · rw [← rankD_eq, h₃.1]; exact Nat.lt_succ_of_lt this
     · exact this
 
 theorem setParent_rankD_lt {arr : Array UFNode} {x y : Fin arr.size}
-    (h : (arr.get x).rank < (arr.get y).rank) {i : Nat}
+    (h : arr[x.1].rank < arr[y.1].rank) {i : Nat}
     (rankD_lt : parentD arr i ≠ i → rankD arr i < rankD arr (parentD arr i)) :
-    let arr' := arr.set x ⟨y, (arr.get x).rank⟩
+    let arr' := arr.set x ⟨y, arr[x].rank⟩
     parentD arr' i ≠ i → rankD arr' i < rankD arr' (parentD arr' i) :=
   setParentBump_rankD_lt (.inl h) (Nat.le_of_lt h) rankD_lt parentD_set
     (by simp [rankD_set, Nat.ne_of_lt h, rankD_eq, -Array.get_eq_getElem])
@@ -505,7 +501,7 @@ def link (self : UnionFind) (x y : Fin self.size) (yroot : self.parent y = y) :
     · exact self.parentD_lt h
     · rw [parentD_set]; split <;> [exact x.2; exact self.parentD_lt h]
     · rw [parentD_set]; split
-      · exact self.parent'_lt _
+      · exact self.parent'_lt ..
       · rw [parentD_set]; split <;> [exact y.2; exact self.parentD_lt h]
     · rw [parentD_set]; split <;> [exact y.2; exact self.parentD_lt h]
   rankD_lt := by
diff --git a/Batteries/Data/UnionFind/Lemmas.lean b/Batteries/Data/UnionFind/Lemmas.lean
index 9a7b0dac58..f070a6d4f1 100644
--- a/Batteries/Data/UnionFind/Lemmas.lean
+++ b/Batteries/Data/UnionFind/Lemmas.lean
@@ -43,7 +43,7 @@ theorem parentD_linkAux {self} {x y : Fin self.size} :
     if x.1 = y then
       parentD self i
     else
-      if (self.get y).rank < (self.get x).rank then
+      if self[y.1].rank < self[x.1].rank then
         if y = i then x else parentD self i
       else
         if x = i then y else parentD self i := by
diff --git a/Batteries/Data/Vector/Basic.lean b/Batteries/Data/Vector/Basic.lean
index 0ae5871356..73a4a41aee 100644
--- a/Batteries/Data/Vector/Basic.lean
+++ b/Batteries/Data/Vector/Basic.lean
@@ -68,7 +68,7 @@ instance [Inhabited α] : Inhabited (Vector α n) where
 
 /-- Get an element of a vector using a `Fin` index. -/
 @[inline] def get (v : Vector α n) (i : Fin n) : α :=
-  v.toArray.get (i.cast v.size_toArray.symm)
+  v.toArray[(i.cast v.size_toArray.symm).1]
 
 /-- Get an element of a vector using a `USize` index and a proof that the index is within bounds. -/
 @[inline] def uget (v : Vector α n) (i : USize) (h : i.toNat < n) : α :=
diff --git a/BatteriesTest/array.lean b/BatteriesTest/array.lean
index 89f784293e..58bb65b713 100644
--- a/BatteriesTest/array.lean
+++ b/BatteriesTest/array.lean
@@ -9,7 +9,7 @@ variable (v d : α)
 variable (g : i < (a.set! i v).size)
 variable (j_lt : j < (a.set! i v).size)
 
-#check_simp (a.set! i v).get ⟨i, g⟩ ~> v
+#check_simp (a.set! i v).get i g ~> v
 #check_simp (a.set! i v).get! i ~> (a.setD i v)[i]!
 #check_simp (a.set! i v).getD i d ~> if i < a.size then v else d
 #check_simp (a.set! i v)[i] ~> v
diff --git a/lean-toolchain b/lean-toolchain
index 0bef727630..9e0b2f2e74 100644
--- a/lean-toolchain
+++ b/lean-toolchain
@@ -1 +1 @@
-leanprover/lean4:v4.14.0-rc1
+leanprover/lean4:nightly-2024-11-12