diff --git a/Iris/Iris/Std/HeapInstances.lean b/Iris/Iris/Std/HeapInstances.lean
index 1251674f3..21398e538 100644
--- a/Iris/Iris/Std/HeapInstances.lean
+++ b/Iris/Iris/Std/HeapInstances.lean
@@ -84,32 +84,6 @@ end ClassicalAllocHeap
 
 end Iris.Std
 
-section Lemmas
-
-/-- Merge an optional value with an optional key-value pair, using the pair's key in the
-merge function. This is an internal helper for TreeMap heap proofs. -/
-private def Option.pairMerge (f : K → V → V → V) (o1 : Option V)
-    (o2 : Option (K × V)) : Option V :=
-  o2.elim o1 fun ⟨k, v2⟩ => some (o1.elim v2 (f k · v2))
-
-@[simp]
-private theorem Option.pairMerge_none_right : pairMerge f o1 none = o1 := by
-  cases o1 <;> rfl
-
-@[simp]
-private theorem Option.pairMerge_some_right :
-    pairMerge f o1 (some (k, v)) = merge (f k) o1 (some v) := by
-  cases o1 <;> rfl
-
-/-- Insert a value if none, or merge with existing value. Used in alter operations for
-maps. This is `Option.merge f o (some v)` - inserting `v` when empty, or merging with
-existing. -/
-@[simp]
-def Option.insertOrMerge (f : V → V → V) (v : V) (o : Option V) : Option V :=
-  merge f o (some v)
-
-end Lemmas
-
 namespace Std.TreeMap
 
 /-! ## TreeMap Heap Instance -/
@@ -120,106 +94,20 @@ open Option Std.DTreeMap.Internal.Impl List TransCmp OrientedCmp LawfulEqCmp Ord
 open Iris.Std
 
 variable {K V : Type _} [Ord K] [TransOrd K] [LawfulEqOrd K]
-
-private theorem get?_foldl_alter_impl_sigma {l : List ((_ : K) × V)}
-    (hinit : init.WF) (hl : l.Pairwise (fun x y => ¬ (compare x.1 y.1).isEq)) :
-    Const.get? (l.foldl (fun acc ⟨k, v⟩ => Const.alter! k (insertOrMerge (f k) v) acc) init) k =
-      pairMerge f (Const.get? init k)
-        ((l.find? (fun x => (compare x.1 k).isEq)).map (fun kv => (kv.1, kv.2))) := by
-  induction l generalizing init with
-  | nil =>
-    simp [List.foldl_nil]
-  | cons hd tl IH =>
-    rw [List.foldl_cons, IH (WF.constAlter! hinit) (hl.tail), Const.get?_alter! hinit]
-    by_cases h : compare hd.1 k = .eq <;> simp [h]
-    rw [← Const.get?_congr hinit h]
-    have hhead_none : tl.find? (fun x => (compare x.1 k).isEq) = none := by
-      refine List.find?_eq_none.mpr fun _ hkv He => List.rel_of_pairwise_cons hl hkv ?_
-      refine isEq_iff_eq_eq.mpr <| compare_eq_iff_eq.mpr ?_
-      rw [eq_of_compare h, compare_eq_iff_eq.mp <| isEq_iff_eq_eq.mp He]
-    rw [hhead_none, map_none, pairMerge_none_right]
-
-private theorem getElem?_foldl_alter {l : List (K × V)} {init : TreeMap K V compare}
-    (hl : l.Pairwise (fun a b => compare a.1 b.1 ≠ .eq)) :
-    (l.foldl (fun acc kv => acc.alter kv.1 (insertOrMerge (f kv.1) kv.2)) init)[k]? =
-      pairMerge f init[k]? (l.find? (fun kv => (compare kv.1 k).isEq)) := by
-  induction l generalizing init with
-  | nil =>
-    simp
-  | cons hd tl ih =>
-    rw [List.foldl_cons, ih (hl.tail)]
-    by_cases heq : compare hd.1 k = .eq
-    · have htl : tl.find? (fun kv => (compare kv.1 k).isEq) = none := by
-        refine List.find?_eq_none.mpr fun kv hkv h => ?_
-        refine List.rel_of_pairwise_cons hl hkv (eq_trans heq ?_)
-        rw [compare_eq_iff_eq.mp <| isEq_iff_eq_eq.mp h]
-        exact compare_self
-      simp [getElem?_congr (eq_symm heq), htl, heq]
-      cases _ : init[hd.1]? <;> rfl
-    · simp [getElem?_alter, heq]
-
-private theorem getElem?_mergeWith_eq_foldl {t₁ t₂ : TreeMap K V compare}
-    {f : K → V → V → V} {k : K} :
-    (t₁.mergeWith f t₂)[k]? =
-      (t₂.toList.foldl (fun acc kv => acc.alter kv.1 (insertOrMerge (f kv.1) kv.2)) t₁)[k]? := by
-  rw [getElem?_foldl_alter (distinct_keys_toList (t := t₂))]
-  rw [show _[_]? = _ from
-    congrArg (Const.get? · k) (Const.mergeWith_eq_mergeWith! ..)]
-  have h_foldl :
-      Const.mergeWith! f t₁.inner.inner t₂.inner.inner =
-        .foldl (fun t a b₂ => Const.alter! a (insertOrMerge (f a) b₂) t)
-          t₁.inner.inner t₂.inner.inner := by
-    unfold Const.mergeWith!
-    congr
-    funext _ _ _
-    congr
-    funext o
-    cases o <;> rfl
-  rw [h_foldl]
-  rw [foldl_eq_foldl]
-  rw [show t₂.toList = _ from Const.toList_eq_toListModel_map]
-  have hfind_map : ∀ l : List ((_ : K) × V),
-      (l.map (fun e => (e.1, e.2))).find? (fun kv => (compare kv.1 k).isEq) =
-        (l.find? (fun kv => (compare kv.1 k).isEq)).map (fun e => (e.1, e.2)) :=
-    fun l => by induction l with grind [isEq]
-  rw [hfind_map]
-  refine get?_foldl_alter_impl_sigma t₁.inner.wf ?_
-  refine (List.pairwise_map.mp <|
-    SameKeys.ordered_iff_pairwise_keys.mp t₂.inner.wf.ordered).imp ?_
-  rintro hlt heq H
-  simp [H]
+attribute [local instance low] beqOfOrd
 
 @[simp]
 theorem getElem?_mergeWith' {t₁ t₂ : TreeMap K V compare} {f : K → V → V → V} {k : K} :
     (t₁.mergeWith f t₂)[k]? = merge (f k) t₁[k]? t₂[k]? := by
-  rw [getElem?_mergeWith_eq_foldl (t₁ := t₁) (t₂ := t₂) (f := f) (k := k),
-      getElem?_foldl_alter (distinct_keys_toList (t := t₂))]
-  cases h : t₂[k]? with
-  | none =>
-    rw [List.find?_eq_none.mpr, pairMerge_none_right, merge_none_right]
-    refine fun ⟨k', v'⟩ hkv' heq => ?_
-    have _ :=
-      (getElem?_eq_some_iff_exists_compare_eq_eq_and_mem_toList (k := k) (v := v')).mpr
-        ⟨k', ?G, hkv'⟩
-    case G =>
-      replace h := compare_eq_iff_eq.mp <| isEq_iff_eq_eq.mp heq
-      simp only [isEq_iff_eq_eq, compare_eq_iff_eq] at heq
-      exact heq ▸ compare_self
-    grind
-  | some v =>
-    obtain ⟨k', hcmp, hmem⟩ :=
-      getElem?_eq_some_iff_exists_compare_eq_eq_and_mem_toList.mp h
-    have hpred : (compare k' k).isEq = true := by simp [eq_symm hcmp]
-    obtain ⟨kv, hfind⟩ := isSome_iff_exists.mp <|
-      List.find?_isSome (p := fun kv => (compare kv.1 k).isEq) |>.mpr ⟨(k', v), hmem, hpred⟩
-    have hkv_cmp : compare kv.1 k = .eq := by
-      simpa [beq_iff_eq] using List.find?_some hfind
-    have hval : kv.2 = v := by grind
-    have hfind : List.find? (fun kv => (compare kv.fst k).isEq) t₂.toList =
-        some (kv.fst, v) := by
-      simp [← hval, ← hfind]
-    simp [← hval, hfind]
-    simp [eq_of_compare hkv_cmp]
+  change Const.get? (Const.mergeWith f t₁.inner.inner t₂.inner.inner
+    t₁.inner.wf.balanced).impl k =
+    merge (f k) (Const.get? t₁.inner.inner k) (Const.get? t₂.inner.inner k)
+  have ht₁ : t₁.inner.inner.WF := t₁.inner.wf
+  have ht₂ : t₂.inner.inner.WF := t₂.inner.wf
+  have hmerge : (Const.mergeWith f t₁.inner.inner t₂.inner.inner
+      t₁.inner.wf.balanced).impl.WF := t₁.inner.wf.constMergeWith
+  simp_to_model [Const.mergeWith, Const.get?] using
+    Std.Internal.List.Const.getValue?_mergeWith
 
 end HeapInstance