diff --git a/Complexity.lean b/Complexity.lean
index f08f52b9d2..d9741329c7 100644
--- a/Complexity.lean
+++ b/Complexity.lean
@@ -2810,6 +2810,7 @@ public import Complexity.Foundations.Probability.Gaussian.Sheppard
 public import Complexity.Foundations.Probability.HeavyCount
 public import Complexity.Foundations.Probability.HeavyCountRarity
 public import Complexity.Foundations.Probability.HierarchyParams
+public import Complexity.Foundations.Probability.PolynomialAtomCutoffs
 public import Complexity.Foundations.Probability.ProductError
 public import Complexity.Foundations.Probability.RootMetric
 public import Complexity.Foundations.Probability.SecondMoment
diff --git a/Complexity/Foundations/Probability/PolynomialAtomCutoffs.lean b/Complexity/Foundations/Probability/PolynomialAtomCutoffs.lean
new file mode 100644
index 0000000000..52858c0ed9
--- /dev/null
+++ b/Complexity/Foundations/Probability/PolynomialAtomCutoffs.lean
@@ -0,0 +1,294 @@
+/-
+Copyright (c) 2026 Christian Reitwiessner, Samuel Schlesinger. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Christian Reitwiessner, Samuel Schlesinger
+-/
+
+module
+-- upstream: candidate
+
+public import Complexity.Foundations.Analysis.SpecialFunctions.PolynomialSwitch
+import Mathlib.Tactic.Linarith
+import Mathlib.Tactic.Positivity
+import Mathlib.Tactic.Ring
+
+/-!
+# Polynomial preparation, score, and witness cutoffs
+
+These are concrete polynomial versions of the atom threshold template in
+[OpenAI2026LogSpace, (5.5)] and the broad witness in the proof of its support-margin lemma.
+For a fixed support scale `θ > 0`, they define the preparation `hθ(v) Rθ(r)`, auxiliary score
+`Iθ(v,r)`, and witness `Jθ(v,r)`. They take values in `[0,1]`, have globally Lipschitz fourth
+roots jointly in the entry and rank, and use rational arithmetic when their inputs are rational.
+
+Their entry-zero and rank-closure thresholds `(e,g)` are respectively
+`(θ/2, θ/500)`, `(θ/8, θ/50)`, and `(82θ/1000, 27θ/1000)`. Each has `3g < e`, including the
+witness's strict margin `θ/1000`. All rank factors are one near zero. These are scalar laws for
+the concrete row functions, suitable for the stationary-reference compression comparison.
+The first argument is the full raw entry and the second is the prescribed full-row rank;
+only function evaluation applies the switches' scalar clipping.
+
+This is the fourth-moment adaptation in complexitylib issue #1721. The pinned preprint uses
+eighth roots. These polynomial cutoffs do not replace the existing exponential `AtomCutoffs`
+API, which proves regularity for every positive power. Normalized main atom functions, access
+enumeration, eighth-root regularity, and machine-resource bounds are separate obligations.
+
+## Main definitions
+
+* `Cslib.polynomialPrepCutoff4`, `Cslib.polynomialRowCutoff4`: the preparatory and row factors.
+* `Cslib.polynomialPrepRow4`, `Cslib.polynomialAuxCutoff4`, `Cslib.polynomialWitnessCutoff4`:
+  the three concrete pre-incoming row functions.
+
+## Main results
+
+* The endpoint, rank-flatness, and range lemmas for each function.
+* `Cslib.exists_abs_polynomialPrepRow4_root_sub_le`,
+  `Cslib.exists_abs_polynomialAuxCutoff4_root_sub_le`,
+  `Cslib.exists_abs_polynomialWitnessCutoff4_root_sub_le`: joint fourth-root bounds.
+* The `*_ratCast` lemmas: exact compatibility with rational evaluation.
+
+## References
+
+* [OpenAI, *Exact Derandomization of Logarithmic Space: L = RL = BPL*][OpenAI2026LogSpace],
+  Section 5.1, (5.5), support-margin lemma and compression-threshold table in Section 5.5
+  (23 September 2026, revision `7ef5c0cc`, not peer reviewed).
+-/
+
+public section
+
+namespace Cslib
+
+section Definitions
+
+variable {R : Type*} [Field R] [LinearOrder R]
+
+/-- The polynomial preparation factor with transition from `θ/2` to `3θ/4`. -/
+@[expose] def polynomialPrepCutoff4 (θ v : R) : R :=
+  polynomialSwitch4 (θ / 2) (3 * θ / 4) v
+
+/-- The polynomial row gate, full through `θ/1000` and closed from `θ/500`. -/
+@[expose] def polynomialRowCutoff4 (θ r : R) : R :=
+  1 - polynomialSwitch4 (θ / 1000) (θ / 500) r
+
+/-- The actual unnormalized pre-incoming preparation `hθ(v) Rθ(r)`. -/
+@[expose] def polynomialPrepRow4 (θ v r : R) : R :=
+  polynomialPrepCutoff4 θ v * polynomialRowCutoff4 θ r
+
+/-- The auxiliary score with the threshold intervals of [OpenAI2026LogSpace, (5.5)]. -/
+@[expose] def polynomialAuxCutoff4 (θ v r : R) : R :=
+  polynomialSwitch4 (θ / 8) (θ / 4) v *
+    (1 - polynomialSwitch4 (θ / 100) (θ / 50) r)
+
+/-- The broad analytical witness `Jθ` of the support-margin lemma. Its support is not required
+to have a further witness. -/
+@[expose] def polynomialWitnessCutoff4 (θ v r : R) : R :=
+  polynomialSwitch4 (82 * θ / 1000) (90 * θ / 1000) v *
+    (1 - polynomialSwitch4 (26 * θ / 1000) (27 * θ / 1000) r)
+
+end Definitions
+
+variable {θ v r : ℝ}
+
+/-! ## Range and threshold laws -/
+
+theorem polynomialPrepCutoff4_nonneg (θ v : ℝ) : 0 ≤ polynomialPrepCutoff4 θ v :=
+  polynomialSwitch4_nonneg _ _ _
+
+theorem polynomialPrepCutoff4_le_one (θ v : ℝ) : polynomialPrepCutoff4 θ v ≤ 1 :=
+  polynomialSwitch4_le_one _ _ _
+
+theorem polynomialPrepCutoff4_eq_zero (hθ : 0 < θ) (hv : v ≤ θ / 2) :
+    polynomialPrepCutoff4 θ v = 0 := polynomialSwitch4_of_le (by linarith) hv
+
+theorem polynomialPrepCutoff4_eq_one (hθ : 0 < θ) (hv : 3 * θ / 4 ≤ v) :
+    polynomialPrepCutoff4 θ v = 1 := polynomialSwitch4_of_ge (by linarith) hv
+
+theorem polynomialRowCutoff4_nonneg (θ r : ℝ) : 0 ≤ polynomialRowCutoff4 θ r :=
+  sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _)
+
+theorem polynomialRowCutoff4_le_one (θ r : ℝ) : polynomialRowCutoff4 θ r ≤ 1 :=
+  sub_le_self _ (polynomialSwitch4_nonneg _ _ _)
+
+theorem polynomialRowCutoff4_eq_one (hθ : 0 < θ) (hr : r ≤ θ / 1000) :
+    polynomialRowCutoff4 θ r = 1 := by
+  rw [polynomialRowCutoff4, polynomialSwitch4_of_le (by linarith) hr, sub_zero]
+
+theorem polynomialRowCutoff4_eq_zero_iff (hθ : 0 < θ) :
+    polynomialRowCutoff4 θ r = 0 ↔ θ / 500 ≤ r := by
+  rw [polynomialRowCutoff4, sub_eq_zero, eq_comm, polynomialSwitch4_eq_one_iff (by linarith)]
+
+theorem polynomialRowCutoff4_eq_zero (hθ : 0 < θ) (hr : θ / 500 ≤ r) :
+    polynomialRowCutoff4 θ r = 0 := (polynomialRowCutoff4_eq_zero_iff hθ).mpr hr
+
+theorem polynomialPrepRow4_nonneg (θ v r : ℝ) : 0 ≤ polynomialPrepRow4 θ v r :=
+  mul_nonneg (polynomialPrepCutoff4_nonneg _ _) (polynomialRowCutoff4_nonneg _ _)
+
+theorem polynomialPrepRow4_le_one (θ v r : ℝ) : polynomialPrepRow4 θ v r ≤ 1 :=
+  (mul_le_of_le_one_right (polynomialPrepCutoff4_nonneg _ _)
+    (polynomialRowCutoff4_le_one _ _)).trans (polynomialPrepCutoff4_le_one _ _)
+
+theorem polynomialPrepRow4_eq_zero_of_entry_le (hθ : 0 < θ) (hv : v ≤ θ / 2) :
+    polynomialPrepRow4 θ v r = 0 := by
+  rw [polynomialPrepRow4, polynomialPrepCutoff4_eq_zero hθ hv, zero_mul]
+
+theorem polynomialPrepRow4_eq_zero_of_rank_ge (hθ : 0 < θ) (hr : θ / 500 ≤ r) :
+    polynomialPrepRow4 θ v r = 0 := by
+  rw [polynomialPrepRow4, polynomialRowCutoff4_eq_zero hθ hr, mul_zero]
+
+theorem polynomialPrepRow4_of_rank_le (hθ : 0 < θ) (hr : r ≤ θ / 1000) :
+    polynomialPrepRow4 θ v r = polynomialPrepCutoff4 θ v := by
+  rw [polynomialPrepRow4, polynomialRowCutoff4_eq_one hθ hr, mul_one]
+
+theorem polynomialAuxCutoff4_nonneg (θ v r : ℝ) : 0 ≤ polynomialAuxCutoff4 θ v r :=
+  mul_nonneg (polynomialSwitch4_nonneg _ _ _) (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _))
+
+theorem polynomialAuxCutoff4_le_one (θ v r : ℝ) : polynomialAuxCutoff4 θ v r ≤ 1 :=
+  (mul_le_of_le_one_right (polynomialSwitch4_nonneg _ _ _)
+    (sub_le_self _ (polynomialSwitch4_nonneg _ _ _))).trans (polynomialSwitch4_le_one _ _ _)
+
+theorem polynomialAuxCutoff4_eq_zero_of_entry_le (hθ : 0 < θ) (hv : v ≤ θ / 8) :
+    polynomialAuxCutoff4 θ v r = 0 := by
+  rw [polynomialAuxCutoff4, polynomialSwitch4_of_le (by linarith) hv, zero_mul]
+
+theorem polynomialAuxCutoff4_eq_zero_of_rank_ge (hθ : 0 < θ) (hr : θ / 50 ≤ r) :
+    polynomialAuxCutoff4 θ v r = 0 := by
+  rw [polynomialAuxCutoff4, polynomialSwitch4_of_ge (by linarith) hr, sub_self, mul_zero]
+
+theorem polynomialAuxCutoff4_of_rank_le (hθ : 0 < θ) (hr : r ≤ θ / 100) :
+    polynomialAuxCutoff4 θ v r = polynomialSwitch4 (θ / 8) (θ / 4) v := by
+  rw [polynomialAuxCutoff4, polynomialSwitch4_of_le (by linarith) hr, sub_zero, mul_one]
+
+theorem polynomialAuxCutoff4_eq_one (hθ : 0 < θ) (hv : θ / 4 ≤ v) (hr : r ≤ θ / 100) :
+    polynomialAuxCutoff4 θ v r = 1 := by
+  rw [polynomialAuxCutoff4_of_rank_le hθ hr, polynomialSwitch4_of_ge (by linarith) hv]
+
+/-- On the support relevant to the incoming cap, the concrete auxiliary score is one. -/
+theorem polynomialAuxCutoff4_eq_one_of_rowCutoff_ne_zero (hθ : 0 < θ) (hv : θ / 4 ≤ v)
+    (hr : polynomialRowCutoff4 θ r ≠ 0) : polynomialAuxCutoff4 θ v r = 1 := by
+  have hsmall : r < θ / 500 := lt_of_not_ge fun h => hr (polynomialRowCutoff4_eq_zero hθ h)
+  exact polynomialAuxCutoff4_eq_one hθ hv (by linarith)
+
+theorem polynomialWitnessCutoff4_nonneg (θ v r : ℝ) : 0 ≤ polynomialWitnessCutoff4 θ v r :=
+  mul_nonneg (polynomialSwitch4_nonneg _ _ _) (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _))
+
+theorem polynomialWitnessCutoff4_le_one (θ v r : ℝ) : polynomialWitnessCutoff4 θ v r ≤ 1 :=
+  (mul_le_of_le_one_right (polynomialSwitch4_nonneg _ _ _)
+    (sub_le_self _ (polynomialSwitch4_nonneg _ _ _))).trans (polynomialSwitch4_le_one _ _ _)
+
+theorem polynomialWitnessCutoff4_eq_zero_of_entry_le (hθ : 0 < θ) (hv : v ≤ 82 * θ / 1000) :
+    polynomialWitnessCutoff4 θ v r = 0 := by
+  rw [polynomialWitnessCutoff4, polynomialSwitch4_of_le (by linarith) hv, zero_mul]
+
+theorem polynomialWitnessCutoff4_eq_zero_of_rank_ge (hθ : 0 < θ) (hr : 27 * θ / 1000 ≤ r) :
+    polynomialWitnessCutoff4 θ v r = 0 := by
+  rw [polynomialWitnessCutoff4, polynomialSwitch4_of_ge (by linarith) hr, sub_self, mul_zero]
+
+theorem polynomialWitnessCutoff4_of_rank_le (hθ : 0 < θ) (hr : r ≤ 26 * θ / 1000) :
+    polynomialWitnessCutoff4 θ v r = polynomialSwitch4 (82 * θ / 1000) (90 * θ / 1000) v := by
+  rw [polynomialWitnessCutoff4, polynomialSwitch4_of_le (by linarith) hr, sub_zero, mul_one]
+
+theorem polynomialWitnessCutoff4_eq_one (hθ : 0 < θ) (hv : 90 * θ / 1000 ≤ v)
+    (hr : r ≤ 26 * θ / 1000) : polynomialWitnessCutoff4 θ v r = 1 := by
+  rw [polynomialWitnessCutoff4_of_rank_le hθ hr, polynomialSwitch4_of_ge (by linarith) hv]
+
+/-! ## Joint fourth-root regularity -/
+
+private theorem exists_abs_switch_product_root_sub_le (α β γ δ : ℝ) :
+    ∃ C : ℝ, 0 ≤ C ∧ ∀ v r v' r',
+      |(polynomialSwitch4 α β v * (1 - polynomialSwitch4 γ δ r)) ^ (4⁻¹ : ℝ) -
+        (polynomialSwitch4 α β v' * (1 - polynomialSwitch4 γ δ r')) ^ (4⁻¹ : ℝ)| ≤
+          C * (|v - v'| + |r - r'|) := by
+  obtain ⟨Ka, hKa⟩ := exists_lipschitzWith_polynomialSwitch4_root α β
+  obtain ⟨Kb, hKb⟩ := exists_lipschitzWith_one_sub_polynomialSwitch4_root γ δ
+  refine ⟨max (Ka : ℝ) Kb, le_max_of_le_left Ka.2, ?_⟩
+  intro v r v' r'
+  set A : ℝ → ℝ := fun x => polynomialSwitch4 α β x ^ (4⁻¹ : ℝ)
+  set B : ℝ → ℝ := fun x => (1 - polynomialSwitch4 γ δ x) ^ (4⁻¹ : ℝ)
+  have ha0 (x : ℝ) : 0 ≤ A x := Real.rpow_nonneg (polynomialSwitch4_nonneg _ _ _) _
+  have hb0 (x : ℝ) : 0 ≤ B x :=
+    Real.rpow_nonneg (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _)) _
+  have ha1 (x : ℝ) : A x ≤ 1 :=
+    Real.rpow_le_one (polynomialSwitch4_nonneg _ _ _) (polynomialSwitch4_le_one _ _ _)
+      (by norm_num)
+  have hb1 (x : ℝ) : B x ≤ 1 :=
+    Real.rpow_le_one (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _))
+      (sub_le_self _ (polynomialSwitch4_nonneg _ _ _)) (by norm_num)
+  have hda : |A v - A v'| ≤ Ka * |v - v'| := by
+    simpa only [Real.dist_eq] using hKa.dist_le_mul v v'
+  have hdb : |B r - B r'| ≤ Kb * |r - r'| := by
+    simpa only [Real.dist_eq] using hKb.dist_le_mul r r'
+  rw [Real.mul_rpow (polynomialSwitch4_nonneg _ _ _)
+      (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _)),
+    Real.mul_rpow (polynomialSwitch4_nonneg _ _ _)
+      (sub_nonneg.mpr (polynomialSwitch4_le_one _ _ _))]
+  change |A v * B r - A v' * B r'| ≤ _
+  have hsplit : A v * B r - A v' * B r' =
+      (A v - A v') * B r + A v' * (B r - B r') := by ring
+  rw [hsplit]
+  calc
+    _ ≤ |A v - A v'| * B r + A v' * |B r - B r'| := by
+      refine (abs_add_le _ _).trans_eq ?_
+      rw [abs_mul, abs_mul, abs_of_nonneg (hb0 r), abs_of_nonneg (ha0 v')]
+    _ ≤ |A v - A v'| + |B r - B r'| := by
+      exact add_le_add (mul_le_of_le_one_right (abs_nonneg _) (hb1 r))
+        (mul_le_of_le_one_left (abs_nonneg _) (ha1 v'))
+    _ ≤ (Ka : ℝ) * |v - v'| + (Kb : ℝ) * |r - r'| := add_le_add hda hdb
+    _ ≤ max (Ka : ℝ) Kb * (|v - v'| + |r - r'|) := by
+      rw [mul_add]
+      exact add_le_add (mul_le_mul_of_nonneg_right (le_max_left _ _) (abs_nonneg _))
+        (mul_le_mul_of_nonneg_right (le_max_right _ _) (abs_nonneg _))
+
+/-- The actual preparatory row function has a globally Lipschitz fourth root. -/
+theorem exists_abs_polynomialPrepRow4_root_sub_le (θ : ℝ) :
+    ∃ C : ℝ, 0 ≤ C ∧ ∀ v r v' r',
+      |polynomialPrepRow4 θ v r ^ (4⁻¹ : ℝ) - polynomialPrepRow4 θ v' r' ^ (4⁻¹ : ℝ)| ≤
+        C * (|v - v'| + |r - r'|) :=
+  exists_abs_switch_product_root_sub_le _ _ _ _
+
+/-- The actual auxiliary score has a globally Lipschitz fourth root. -/
+theorem exists_abs_polynomialAuxCutoff4_root_sub_le (θ : ℝ) :
+    ∃ C : ℝ, 0 ≤ C ∧ ∀ v r v' r',
+      |polynomialAuxCutoff4 θ v r ^ (4⁻¹ : ℝ) - polynomialAuxCutoff4 θ v' r' ^ (4⁻¹ : ℝ)| ≤
+        C * (|v - v'| + |r - r'|) :=
+  exists_abs_switch_product_root_sub_le _ _ _ _
+
+/-- The broad witness also has a globally Lipschitz fourth root. -/
+theorem exists_abs_polynomialWitnessCutoff4_root_sub_le (θ : ℝ) :
+    ∃ C : ℝ, 0 ≤ C ∧ ∀ v r v' r',
+      |polynomialWitnessCutoff4 θ v r ^ (4⁻¹ : ℝ) -
+        polynomialWitnessCutoff4 θ v' r' ^ (4⁻¹ : ℝ)| ≤ C * (|v - v'| + |r - r'|) :=
+  exists_abs_switch_product_root_sub_le _ _ _ _
+
+/-! ## Exact rational evaluation -/
+
+@[simp, norm_cast]
+theorem polynomialPrepCutoff4_ratCast (θ v : ℚ) :
+    polynomialPrepCutoff4 (θ : ℝ) v = (polynomialPrepCutoff4 θ v : ℚ) := by
+  simp only [polynomialPrepCutoff4, ← polynomialSwitch4_ratCast, Rat.cast_div, Rat.cast_mul,
+    Rat.cast_ofNat]
+
+@[simp, norm_cast]
+theorem polynomialRowCutoff4_ratCast (θ r : ℚ) :
+    polynomialRowCutoff4 (θ : ℝ) r = (polynomialRowCutoff4 θ r : ℚ) := by
+  simp only [polynomialRowCutoff4, Rat.cast_sub, Rat.cast_one, ← polynomialSwitch4_ratCast,
+    Rat.cast_div, Rat.cast_ofNat]
+
+@[simp, norm_cast]
+theorem polynomialPrepRow4_ratCast (θ v r : ℚ) :
+    polynomialPrepRow4 (θ : ℝ) v r = (polynomialPrepRow4 θ v r : ℚ) := by
+  simp only [polynomialPrepRow4, polynomialPrepCutoff4_ratCast, polynomialRowCutoff4_ratCast,
+    Rat.cast_mul]
+
+@[simp, norm_cast]
+theorem polynomialAuxCutoff4_ratCast (θ v r : ℚ) :
+    polynomialAuxCutoff4 (θ : ℝ) v r = (polynomialAuxCutoff4 θ v r : ℚ) := by
+  simp only [polynomialAuxCutoff4, Rat.cast_mul, Rat.cast_sub, Rat.cast_one,
+    ← polynomialSwitch4_ratCast, Rat.cast_div, Rat.cast_ofNat]
+
+@[simp, norm_cast]
+theorem polynomialWitnessCutoff4_ratCast (θ v r : ℚ) :
+    polynomialWitnessCutoff4 (θ : ℝ) v r = (polynomialWitnessCutoff4 θ v r : ℚ) := by
+  simp only [polynomialWitnessCutoff4, Rat.cast_mul, Rat.cast_sub, Rat.cast_one,
+    ← polynomialSwitch4_ratCast, Rat.cast_div, Rat.cast_ofNat]
+
+end Cslib
diff --git a/ComplexityTests/PolynomialAtomCutoffs.lean b/ComplexityTests/PolynomialAtomCutoffs.lean
new file mode 100644
index 0000000000..917ce9d985
--- /dev/null
+++ b/ComplexityTests/PolynomialAtomCutoffs.lean
@@ -0,0 +1,88 @@
+/-
+Copyright (c) 2026 Samuel Schlesinger. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Samuel Schlesinger
+-/
+
+import Complexity.Foundations.Probability.PolynomialAtomCutoffs
+import Complexity.Foundations.Probability.CorrectionAtom
+import Mathlib.LinearAlgebra.Matrix.Notation
+import Mathlib.Tactic.Linarith
+import Mathlib.Tactic.NormNum
+
+/-!
+# Tests for polynomial atom cutoffs
+
+Both switches vary in each interior example, producing exact value `1/4`. The broad witness
+retains its strict entry/rank margin at its closed endpoints. Concrete existing atom and score
+expressions use the new polynomial factors, and the witness's fourth-root variation forces
+its Lipschitz constant to be positive.
+-/
+
+namespace ComplexityTests.PolynomialAtomCutoffs
+
+open Cslib Finset Matrix
+
+-- All three functions execute with rational inputs, including both transition regions.
+/-- info: true -/
+#guard_msgs in
+#eval [polynomialPrepRow4 (8 : ℚ) 5 (3 / 250),
+    polynomialAuxCutoff4 (8 : ℚ) (3 / 2) (3 / 25),
+    polynomialWitnessCutoff4 (1000 : ℚ) 86 (53 / 2)] == [1 / 4, 1 / 4, 1 / 4]
+
+private theorem witness_quarter : polynomialWitnessCutoff4 (1000 : ℚ) 86 (53 / 2) = 1 / 4 := by
+  norm_num [polynomialWitnessCutoff4, polynomialSwitch4, polynomialTransition4,
+    transitionPolynomial4]
+
+-- Rational evaluation is exactly the real function used by the analytic theorems.
+example : polynomialWitnessCutoff4 (1000 : ℝ) 86 (53 / 2) = 1 / 4 := by
+  have h := polynomialWitnessCutoff4_ratCast 1000 86 (53 / 2)
+  norm_num only [Rat.cast_ofNat, Rat.cast_div, witness_quarter] at h
+  exact h
+
+example : polynomialPrepRow4 (8 : ℝ) (-4) (-1) = 0 ∧
+    polynomialAuxCutoff4 (8 : ℝ) (-4) (-1) = 0 ∧
+    polynomialWitnessCutoff4 (1000 : ℝ) (-4) (-1) = 0 := by
+  exact ⟨polynomialPrepRow4_eq_zero_of_entry_le (by norm_num) (by norm_num),
+    polynomialAuxCutoff4_eq_zero_of_entry_le (by norm_num) (by norm_num),
+    polynomialWitnessCutoff4_eq_zero_of_entry_le (by norm_num) (by norm_num)⟩
+
+-- The exact witness margin is 82 - 3*27 = 1; closure includes both boundary points.
+example : (3 : ℝ) * 27 < 82 ∧ polynomialWitnessCutoff4 (1000 : ℝ) 82 0 = 0 ∧
+    polynomialWitnessCutoff4 (1000 : ℝ) 90 27 = 0 ∧
+    polynomialWitnessCutoff4 (1000 : ℝ) 90 26 = 1 := by
+  exact ⟨by norm_num,
+    polynomialWitnessCutoff4_eq_zero_of_entry_le (by norm_num) (by norm_num),
+    polynomialWitnessCutoff4_eq_zero_of_rank_ge (by norm_num) (by norm_num),
+    polynomialWitnessCutoff4_eq_one (by norm_num) (by norm_num) (by norm_num)⟩
+
+private noncomputable def G : Matrix (Fin 2) (Fin 2) ℝ := !![0, 8; 0, 0]
+
+private theorem first_row_rank : kthLargest 2 univ (fun y => G 0 y / 1) = 0 := by
+  norm_num [kthLargest, G, Fin.univ_succ, filter_insert, filter_singleton]
+
+-- This is an actual atom preparation and actual auxiliary score, not separate scalar formulas.
+example : atomPrep (polynomialPrepCutoff4 8) (polynomialRowCutoff4 8) 2 1 G univ 0 1 = 1 ∧
+    auxScore (polynomialAuxCutoff4 8) 2 1 G univ 0 1 = 1 := by
+  constructor
+  · rw [atomPrep, rowGate, first_row_rank]
+    have hv : G 0 1 / 1 = 8 := by norm_num [G]
+    rw [hv, polynomialPrepCutoff4_eq_one (by norm_num) (by norm_num),
+      polynomialRowCutoff4_eq_one (by norm_num) (by norm_num), mul_one]
+  · rw [auxScore, first_row_rank]
+    have hv : G 0 1 / 1 = 8 := by norm_num [G]
+    rw [hv]
+    exact polynomialAuxCutoff4_eq_one (by norm_num) (by norm_num) (by norm_num)
+
+-- The analytic constant cannot be zero: the fourth root changes from zero to one over width 8.
+example : ∃ C : ℝ, 1 / 8 ≤ C ∧ ∀ v r v' r',
+    |polynomialWitnessCutoff4 1000 v r ^ (4⁻¹ : ℝ) -
+      polynomialWitnessCutoff4 1000 v' r' ^ (4⁻¹ : ℝ)| ≤ C * (|v - v'| + |r - r'|) := by
+  obtain ⟨C, _, hC⟩ := exists_abs_polynomialWitnessCutoff4_root_sub_le 1000
+  have h := hC 90 0 82 0
+  rw [polynomialWitnessCutoff4_eq_one (by norm_num) (by norm_num) (by norm_num),
+    polynomialWitnessCutoff4_eq_zero_of_entry_le (by norm_num) (by norm_num)] at h
+  norm_num at h
+  exact ⟨C, by linarith, hC⟩
+
+end ComplexityTests.PolynomialAtomCutoffs