diff --git a/OpenGALib.lean b/OpenGALib.lean
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--- a/OpenGALib.lean
+++ b/OpenGALib.lean
@@ -1,4 +1,5 @@
 import OpenGALib.Algebraic
+import OpenGALib.Manifold
 import OpenGALib.Tensor
 import OpenGALib.MetricGeometry
 import OpenGALib.Riemannian
diff --git a/OpenGALib/Manifold.lean b/OpenGALib/Manifold.lean
new file mode 100644
index 0000000..f63f740
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+++ b/OpenGALib/Manifold.lean
@@ -0,0 +1,10 @@
+import OpenGALib.Manifold.Charts.CoordinateBall
+
+/-!
+# Manifold
+
+Manifold-foundations domain: chart-level and atlas-level structure on
+topological and smooth manifolds, stated directly on Mathlib's
+`ChartedSpace` / `IsManifold` API. Sits below `Riemannian` in the library
+layering. Currently provides coordinate-ball predicates for charts.
+-/
diff --git a/OpenGALib/Manifold/Charts/CoordinateBall.lean b/OpenGALib/Manifold/Charts/CoordinateBall.lean
new file mode 100644
index 0000000..56de54a
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+++ b/OpenGALib/Manifold/Charts/CoordinateBall.lean
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+import Mathlib.Analysis.InnerProductSpace.PiL2
+import Mathlib.Geometry.Manifold.ChartedSpace
+import Mathlib.Geometry.Manifold.ContMDiff.Atlas
+import Mathlib.Geometry.Manifold.Instances.Real
+import Mathlib.Topology.Bases
+import Mathlib.Topology.Separation.Basic
+
+/-!
+# Coordinate balls
+
+Chart-shape predicates and constructions, layered by how much ambient
+structure they need so downstream code imports only the generality it uses:
+
+1. **Model-generic** — `IsCoordinateBall` is stated over any metric model
+   space, not just `EuclideanSpace`; it is the reusable base every other
+   layer builds on.
+2. **Euclidean charts** — `IsCenteredAt`, `IsCoordinateBox`, `centerAt`
+   need coordinates and an origin, so they specialise to the Euclidean model.
+3. **Smooth-manifold layer** — `IsSmoothCoordinateBall` and
+   `IsRegularCoordinateBall` build on the maximal smooth atlas; these are the
+   interface consumed by covering and partition-of-unity arguments. The
+   "collar room" of a regular coordinate ball is the reusable payload; the
+   predicate itself is mostly a stepping stone to
+   `IsRegularCoordinateBall.exists_smoothCoordinateBall_superset`.
+
+## Main definitions
+
+* `OpenPartialHomeomorph.IsCoordinateBall` — the chart's image is an open metric ball.
+* `OpenPartialHomeomorph.IsCenteredAt` — the chart sends the point to `0`.
+* `OpenPartialHomeomorph.IsCoordinateBox` — the chart's image is a product of open intervals.
+* `OpenPartialHomeomorph.centerAt` — translate a chart so a source point maps to `0`.
+* `Manifold.IsSmoothCoordinateBall` — source of a maximal-atlas chart whose image is an open ball.
+* `Manifold.IsRegularCoordinateBall` — a coordinate ball whose closure sits in a larger chart.
+
+## Main results
+
+* `OpenPartialHomeomorph.isCoordinateBall_of_target_eq_ball` — a chart with ball image is a coordinate ball.
+* `OpenPartialHomeomorph.isCoordinateBox_of_target_eq` — a chart with box image is a coordinate box.
+* `OpenPartialHomeomorph.centerAt_isCenteredAt` — the centered chart is centered at its point.
+* `Manifold.IsRegularCoordinateBall.exists_smoothCoordinateBall_superset` — a regular
+  coordinate ball lies in a surrounding smooth coordinate ball.
+
+Provenance: SmoothManifoldsLee a5f308c — Definition_1_extra_2, Definition_1_3_extra_1.
+-/
+
+noncomputable section
+
+open Set
+open scoped Manifold Topology
+
+universe u v
+
+section Charts
+
+variable {H : Type*} [PseudoMetricSpace H]
+variable {n : ℕ} {M : Type u} [TopologicalSpace M]
+
+/-- **Math.** The chart `e` is a *coordinate ball*: its image is an open metric ball
+`Metric.ball c r` of positive radius. Stated over any metric model space, so it
+applies beyond `EuclideanSpace`. -/
+def OpenPartialHomeomorph.IsCoordinateBall (e : OpenPartialHomeomorph M H) : Prop :=
+  ∃ c : H, ∃ r : ℝ, 0 < r ∧ e.target = Metric.ball c r
+
+/-- **Math.** A chart whose image is a given open ball `Metric.ball c r` is a
+coordinate ball. -/
+theorem OpenPartialHomeomorph.isCoordinateBall_of_target_eq_ball
+    (e : OpenPartialHomeomorph M H) (c : H) (r : ℝ) (hr : 0 < r)
+    (h : e.target = Metric.ball c r) : e.IsCoordinateBall :=
+  ⟨c, r, hr, h⟩
+
+variable (e : OpenPartialHomeomorph M (EuclideanSpace ℝ (Fin n)))
+
+/-- **Math.** The chart `e` is *centered at* `p`: the point `p` lies in its source
+and `e` sends it to the origin `0`. -/
+def OpenPartialHomeomorph.IsCenteredAt (p : M) : Prop :=
+  p ∈ e.source ∧ e p = 0
+
+/-- **Math.** The chart `e` is a *coordinate box*: its image is a product of open
+intervals `∏ᵢ (aᵢ, bᵢ)`. -/
+def OpenPartialHomeomorph.IsCoordinateBox : Prop :=
+  ∃ a b : EuclideanSpace ℝ (Fin n),
+    (∀ i, a i < b i) ∧ e.target = { x | ∀ i : Fin n, x i ∈ Set.Ioo (a i) (b i) }
+
+/-- **Math.** A chart whose image is a given open box `∏ᵢ (aᵢ, bᵢ)` is a coordinate
+box. -/
+theorem OpenPartialHomeomorph.isCoordinateBox_of_target_eq
+    (e : OpenPartialHomeomorph M (EuclideanSpace ℝ (Fin n)))
+    (a b : EuclideanSpace ℝ (Fin n))
+    (hab : ∀ i, a i < b i)
+    (h : e.target = { x | ∀ i : Fin n, x i ∈ Set.Ioo (a i) (b i) }) : e.IsCoordinateBox :=
+  ⟨a, b, hab, h⟩
+
+/-- **Math.** *Center* the chart `e` at a source point `p`: the chart with the same
+source that sends `p` to the origin. -/
+def OpenPartialHomeomorph.centerAt (p : e.source) :
+    OpenPartialHomeomorph M (EuclideanSpace ℝ (Fin n)) :=
+  e.transHomeomorph (Homeomorph.addRight (-e p))
+
+/-- **Math.** Centering a chart leaves its domain of definition unchanged. -/
+@[simp] theorem OpenPartialHomeomorph.centerAt_source (p : e.source) :
+    (e.centerAt p).source = e.source :=
+  rfl
+
+/-- **Math.** The chart obtained by centering `e` at `p` is centered at `p`. -/
+theorem OpenPartialHomeomorph.centerAt_isCenteredAt (p : e.source) :
+    (e.centerAt p).IsCenteredAt p := by
+  exact ⟨p.2, by simp [OpenPartialHomeomorph.centerAt]⟩
+
+end Charts
+
+namespace Manifold
+
+variable {E : Type u} [NormedAddCommGroup E] [NormedSpace ℝ E]
+variable {M : Type v} [TopologicalSpace M] [ChartedSpace E M]
+variable [IsManifold (modelWithCornersSelf ℝ E) (⊤ : WithTop ℕ∞) M]
+
+/-- **Math.** A *smooth coordinate ball* is a subset `B ⊆ M` that is the source of a
+chart in the maximal smooth atlas whose image is an open metric ball in the model
+space `E`. -/
+def IsSmoothCoordinateBall (E : Type u) [NormedAddCommGroup E] [NormedSpace ℝ E]
+    {M : Type v} [TopologicalSpace M] [ChartedSpace E M]
+    [IsManifold (modelWithCornersSelf ℝ E) (⊤ : WithTop ℕ∞) M] (B : Set M) : Prop :=
+  ∃ φ : OpenPartialHomeomorph M E,
+    φ ∈ IsManifold.maximalAtlas (modelWithCornersSelf ℝ E) (⊤ : WithTop ℕ∞) M ∧
+      φ.source = B ∧ φ.IsCoordinateBall
+
+/-- **Math.** A *regular coordinate ball* is a subset `B` with collar room: a
+maximal-atlas chart sends `B` to an open ball of radius `r`, its closure to the
+concentric closed ball of radius `r`, and the whole chart image to a strictly
+larger ball of radius `r' > r`. -/
+def IsRegularCoordinateBall (E : Type u) [NormedAddCommGroup E] [NormedSpace ℝ E]
+    {M : Type v} [TopologicalSpace M] [ChartedSpace E M]
+    [IsManifold (modelWithCornersSelf ℝ E) (⊤ : WithTop ℕ∞) M] (B : Set M) : Prop :=
+  ∃ chart : OpenPartialHomeomorph M E,
+    chart ∈ IsManifold.maximalAtlas (modelWithCornersSelf ℝ E) (⊤ : WithTop ℕ∞) M ∧
+      closure B ⊆ chart.source ∧
+      ∃ r r' : ℝ,
+        0 < r ∧
+          r < r' ∧
+          chart '' B = Metric.ball (0 : E) r ∧
+          chart '' closure B = Metric.closedBall (0 : E) r ∧
+          chart.target = Metric.ball (0 : E) r'
+
+/-- **Math.** Every regular coordinate ball is contained in a surrounding smooth
+coordinate ball — the source of its defining larger chart, which contains the
+closure of `B`. -/
+theorem IsRegularCoordinateBall.exists_smoothCoordinateBall_superset {B : Set M}
+    (hB : IsRegularCoordinateBall E B) :
+    ∃ B' : Set M, IsSmoothCoordinateBall E B' ∧ closure B ⊆ B' := by
+  rcases hB with ⟨chart, hchart, hclosure, r, r', hr, hr', -, -, htarget⟩
+  refine ⟨chart.source, ⟨chart, hchart, rfl, ?_⟩, hclosure⟩
+  exact chart.isCoordinateBall_of_target_eq_ball (0 : E) r' (lt_trans hr hr') htarget
+
+end Manifold