From 375b551ed6e52ae047f2a08730404ffe7a5f6b8d Mon Sep 17 00:00:00 2001
From: LehengChen <chenlh@pku.edu.cn>
Date: Mon, 15 Jun 2026 16:53:20 +0800
Subject: [PATCH] port(curve-velocity-mfderiv): re-style to OpenGA house style;
 camelCase def names
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Re-style curve-velocity / mfderiv landing files to corrected house style and
fix snake_case def names per NAMING_CONVENTION §3.

- Rename defs curve_velocity → curveVelocity, curve_velocityWithin →
  curveVelocityWithin; rename bridge theorem to curveVelocityWithin_eq_curveVelocity.
- Module docstrings re-layered by architecture; single Provenance: line each.
- Drop **Eng.** from every declaration docstring; keep **Math.**.
- Statements and proof bodies otherwise unchanged (modulo renames).
- Index OpenGALib/Manifold.lean imports both Tangent modules (alphabetical).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 OpenGALib/Manifold.lean                       |   2 +
 OpenGALib/Manifold/Tangent/CurveVelocity.lean |  78 ++++++++
 OpenGALib/Manifold/Tangent/MFDeriv.lean       | 167 ++++++++++++++++++
 3 files changed, 247 insertions(+)
 create mode 100644 OpenGALib/Manifold/Tangent/CurveVelocity.lean
 create mode 100644 OpenGALib/Manifold/Tangent/MFDeriv.lean

diff --git a/OpenGALib/Manifold.lean b/OpenGALib/Manifold.lean
index 859185d..7ed60b0 100644
--- a/OpenGALib/Manifold.lean
+++ b/OpenGALib/Manifold.lean
@@ -2,6 +2,8 @@ import OpenGALib.Manifold.Charts.ChartedSpaceCore
 import OpenGALib.Manifold.Charts.CoordinateBall
 import OpenGALib.Manifold.Charts.PrecompactBasis
 import OpenGALib.Manifold.Cutoff.Exhaustion
+import OpenGALib.Manifold.Tangent.CurveVelocity
+import OpenGALib.Manifold.Tangent.MFDeriv
 
 /-!
 # Manifold
diff --git a/OpenGALib/Manifold/Tangent/CurveVelocity.lean b/OpenGALib/Manifold/Tangent/CurveVelocity.lean
new file mode 100644
index 0000000..551d2df
--- /dev/null
+++ b/OpenGALib/Manifold/Tangent/CurveVelocity.lean
@@ -0,0 +1,78 @@
+import Mathlib.Geometry.Manifold.Instances.Real
+import Mathlib.Geometry.Manifold.ContMDiff.Basic
+import Mathlib.Geometry.Manifold.MFDeriv.Basic
+
+/-!
+# Velocity of a parametrized curve
+
+Tangent-vector data attached to a smooth curve `γ : ℝ → M`, stated directly on
+Mathlib's manifold-derivative API so it sits at the bottom of the tangent-bundle
+layer with no extra packaging:
+
+1. **Global velocity** — `curveVelocity` pushes the standard unit tangent vector
+   `∂/∂t` through `mfderiv 𝓘(ℝ) I γ t`, the reusable notion of `γ'(t)` consumed
+   wherever a curve's tangent direction is needed.
+2. **Within-set velocity** — `curveVelocityWithin` is the one-sided variant built
+   on `mfderivWithin`, the form used by boundary arguments on a parameter subset
+   `s ⊆ ℝ`. It collapses onto the global velocity exactly where the parameter set
+   is uniquely differentiable and the curve is differentiable, the bridge lemma
+   downstream code relies on to move between the two.
+
+## Main definitions
+
+* `Manifold.curveVelocity` — velocity `γ'(t) ∈ T_{γ t} M` of a curve at `t`.
+* `Manifold.curveVelocityWithin` — within-set velocity relative to a domain
+  subset `s ⊆ ℝ`.
+
+## Main results
+
+* `Manifold.curveVelocityWithin_eq_curveVelocity` — the within-set velocity
+  agrees with the ordinary velocity at a differentiability point of a uniquely
+  differentiable parameter set.
+
+Provenance: SmoothManifoldsLee a5f308c — Definition_3_17_extra_1.
+-/
+
+noncomputable section
+
+open scoped Manifold ContDiff
+
+namespace Manifold
+
+universe uM uH uE
+
+variable
+  {E : Type uE} [NormedAddCommGroup E] [NormedSpace ℝ E]
+  {H : Type uH} [TopologicalSpace H] {I : ModelWithCorners ℝ E H}
+  {M : Type uM} [TopologicalSpace M] [ChartedSpace H M] [IsManifold I ∞ M]
+
+/-- **Math.** The standard unit tangent vector $\partial/\partial t$ at a
+parameter value $t \in \mathbb{R}$, i.e. the number `1` viewed as an element of
+`TangentSpace 𝓘(ℝ) t`. -/
+private abbrev unitTangentVector (t : ℝ) : TangentSpace 𝓘(ℝ) t := (1 : ℝ)
+
+/-- **Math.** The *velocity* of a parametrized curve `γ` at parameter `t` is the
+manifold derivative of `γ` applied to the unit tangent vector `d/dt`, a tangent
+vector in `T_{γ t} M`. -/
+abbrev curveVelocity (I : ModelWithCorners ℝ E H) (γ : ℝ → M) (t : ℝ) :
+    TangentSpace I (γ t) :=
+  mfderiv 𝓘(ℝ) I γ t (unitTangentVector t)
+
+/-- **Math.** The velocity of a parametrized curve at a parameter value computed
+relative to a domain subset `s` of the parameter line — the one-sided/within-set
+variant used for boundary arguments. -/
+abbrev curveVelocityWithin (I : ModelWithCorners ℝ E H) (γ : ℝ → M) (s : Set ℝ) (t : ℝ) :
+    TangentSpace I (γ t) :=
+  mfderivWithin 𝓘(ℝ) I γ s t (unitTangentVector t)
+
+omit [IsManifold I ∞ M] in
+/-- **Math.** On a parameter subset with a unique differential, and at a point
+where the curve is manifold-differentiable, the within-set velocity agrees with
+the ordinary velocity. -/
+theorem curveVelocityWithin_eq_curveVelocity {γ : ℝ → M} {s : Set ℝ} {t : ℝ}
+    (hs : UniqueMDiffWithinAt 𝓘(ℝ) s t) (hγ : MDifferentiableAt 𝓘(ℝ) I γ t) :
+    curveVelocityWithin I γ s t = curveVelocity I γ t := by
+  simpa [curveVelocityWithin, curveVelocity] using
+    DFunLike.congr_fun (mfderivWithin_eq_mfderiv hs hγ) (unitTangentVector t)
+
+end Manifold
diff --git a/OpenGALib/Manifold/Tangent/MFDeriv.lean b/OpenGALib/Manifold/Tangent/MFDeriv.lean
new file mode 100644
index 0000000..d7c52e2
--- /dev/null
+++ b/OpenGALib/Manifold/Tangent/MFDeriv.lean
@@ -0,0 +1,167 @@
+import Mathlib.Geometry.Manifold.ContMDiff.Basic
+import Mathlib.Geometry.Manifold.LocalDiffeomorph
+import Mathlib.Geometry.Manifold.MFDeriv.Basic
+import Mathlib.Geometry.Manifold.MFDeriv.SpecificFunctions
+import Mathlib.Topology.OpenPartialHomeomorph.Constructions
+import Mathlib.Topology.Algebra.Module.Equiv
+
+/-!
+# Functoriality of the manifold differential
+
+The manifold derivative `mfderiv` packaged as the differential of smooth maps,
+stated on Mathlib's `ContMDiff` / `Diffeomorph` API and layered by how the
+differential interacts with structure:
+
+1. **Composition** — the differential is functorial: `mfderiv_comp_of_smooth`
+   is the chain rule `d(G ∘ F)_p = dG_{F p} ∘ dF_p`, the base fact the rest
+   builds on.
+2. **Diffeomorphisms** — for a `C^n` diffeomorphism the differential is a linear
+   isomorphism; `diffeomorph_mfderiv_symm_eq_symm` identifies its inverse with
+   the differential of the inverse map.
+3. **Open submanifolds** — the inclusion of an open subset is a local
+   diffeomorphism, so `mfderiv_open_subset_inclusion_isInvertible` records that
+   its differential is invertible at every point, the interface used when
+   localizing the tangent bundle to an open chart domain.
+
+## Main results
+
+* `Manifold.mfderiv_comp_of_smooth` — chain rule: the differential of a
+  composite of smooth maps is the composite of the differentials.
+* `Manifold.diffeomorph_mfderiv_symm_eq_symm` — for a `C^n` diffeomorphism
+  (`n ≠ 0`), the inverse of the differential is the differential of the inverse.
+* `Manifold.mfderiv_open_subset_inclusion_isInvertible` — the differential of
+  the inclusion of an open subset is invertible at each point.
+
+Provenance: SmoothManifoldsLee a5f308c — Proposition_3_9, Proposition_3_6.
+-/
+
+noncomputable section
+
+open scoped Manifold ContDiff
+
+namespace Manifold
+
+section CompositionAndIdentity
+
+universe u𝕜 uE uE' uE'' uH uH' uH'' uM uN uP
+
+variable {𝕜 : Type u𝕜} [NontriviallyNormedField 𝕜]
+variable {E : Type uE} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
+variable {E' : Type uE'} [NormedAddCommGroup E'] [NormedSpace 𝕜 E']
+variable {E'' : Type uE''} [NormedAddCommGroup E''] [NormedSpace 𝕜 E'']
+variable {H : Type uH} [TopologicalSpace H]
+variable {H' : Type uH'} [TopologicalSpace H']
+variable {H'' : Type uH''} [TopologicalSpace H'']
+variable {I : ModelWithCorners 𝕜 E H}
+variable {I' : ModelWithCorners 𝕜 E' H'}
+variable {I'' : ModelWithCorners 𝕜 E'' H''}
+variable {M : Type uM} [TopologicalSpace M] [ChartedSpace H M] [IsManifold I ∞ M]
+variable {N : Type uN} [TopologicalSpace N] [ChartedSpace H' N] [IsManifold I' ∞ N]
+variable {P : Type uP} [TopologicalSpace P] [ChartedSpace H'' P] [IsManifold I'' ∞ P]
+variable {F : M → N} {G : N → P} {p : M}
+
+omit [IsManifold I ∞ M] [IsManifold I' ∞ N] [IsManifold I'' ∞ P] in
+/-- **Math.** The differential of a composite of smooth maps is the composite of
+the differentials, `d(G ∘ F)_p = dG_{F p} ∘ dF_p`. -/
+theorem mfderiv_comp_of_smooth (hF : ContMDiff I I' ∞ F) (hG : ContMDiff I' I'' ∞ G) :
+    mfderiv I I'' (G ∘ F) p = (mfderiv I' I'' G (F p)).comp (mfderiv I I' F p) := by
+  have hn : (∞ : ℕ∞ω) ≠ 0 := by simp
+  exact mfderiv_comp p (hG.contMDiffAt.mdifferentiableAt hn) (hF.contMDiffAt.mdifferentiableAt hn)
+
+end CompositionAndIdentity
+
+section Diffeomorphisms
+
+universe u𝕜 uE uE' uH uH' uM uN
+
+variable {𝕜 : Type u𝕜} [NontriviallyNormedField 𝕜]
+variable {E : Type uE} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
+variable {E' : Type uE'} [NormedAddCommGroup E'] [NormedSpace 𝕜 E']
+variable {H : Type uH} [TopologicalSpace H]
+variable {H' : Type uH'} [TopologicalSpace H']
+variable {I : ModelWithCorners 𝕜 E H}
+variable {I' : ModelWithCorners 𝕜 E' H'}
+variable {M : Type uM} [TopologicalSpace M] [ChartedSpace H M]
+variable {N : Type uN} [TopologicalSpace N] [ChartedSpace H' N]
+variable {n : ℕ∞ω}
+
+/-- **Math.** For a `C^n` diffeomorphism `Φ` with `n ≠ 0`, the inverse of the
+differential `dΦ_p` is the differential of the inverse diffeomorphism,
+`d(Φ⁻¹)_{Φ p} = (dΦ_p)⁻¹`. -/
+theorem diffeomorph_mfderiv_symm_eq_symm
+    (Φ : M ≃ₘ^n⟮I, I'⟯ N) (hn : n ≠ 0) (p : M) :
+    mfderiv I' I Φ.symm (Φ p) =
+      ((Φ.mfderivToContinuousLinearEquiv hn p).symm :
+        TangentSpace I' (Φ p) →L[𝕜] TangentSpace I p) := by
+  have hΦ : IsLocalDiffeomorphAt I I' n Φ p := Φ.isLocalDiffeomorph p
+  have hlocalInverse : hΦ.localInverse =ᶠ[nhds (Φ p)] Φ.symm := by
+    refine Filter.eventuallyEq_of_mem
+      (hΦ.localInverse_open_source.mem_nhds hΦ.localInverse_mem_source) ?_
+    intro y hy
+    apply Φ.injective
+    simpa using hΦ.localInverse_right_inv hy
+  have h₁ : mfderiv I' I Φ.symm (Φ p) = mfderiv I' I hΦ.localInverse (Φ p) := by
+    symm
+    exact hlocalInverse.mfderiv_eq
+  have h₂ : mfderiv I' I hΦ.localInverse (Φ p) =
+      ((hΦ.mfderivToContinuousLinearEquiv hn).symm :
+        TangentSpace I' (Φ p) →L[𝕜] TangentSpace I p) := rfl
+  have h₃ : ((hΦ.mfderivToContinuousLinearEquiv hn).symm :
+      TangentSpace I' (Φ p) →L[𝕜] TangentSpace I p) =
+      ((Φ.mfderivToContinuousLinearEquiv hn p).symm :
+        TangentSpace I' (Φ p) →L[𝕜] TangentSpace I p) := rfl
+  exact h₁.trans (h₂.trans h₃)
+
+end Diffeomorphisms
+
+section OpenSubsetInclusion
+
+universe u𝕜 uE uH uM
+
+variable {𝕜 : Type u𝕜} [NontriviallyNormedField 𝕜]
+variable {E : Type uE} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
+variable {H : Type uH} [TopologicalSpace H]
+variable {I : ModelWithCorners 𝕜 E H}
+variable {M : Type uM} [TopologicalSpace M] [ChartedSpace H M]
+
+/-- **Math.** If `U` is an open subset of `M`, then for every `p : U` the
+differential of the inclusion `Subtype.val : U → M` at `p` is an isomorphism of
+tangent spaces. -/
+theorem mfderiv_open_subset_inclusion_isInvertible (U : TopologicalSpace.Opens M) (p : U) :
+    (mfderiv I I (Subtype.val : U → M) p).IsInvertible := by
+  let e := U.openPartialHomeomorphSubtypeCoe ⟨p⟩
+  have hsymm : ContMDiffOn I I 1 e.symm (U : Set M) := by
+    intro x hx
+    have hcomp : ContMDiffWithinAt I I 1 (Subtype.val ∘ e.symm) (U : Set M) x := by
+      refine contMDiffWithinAt_id.congr_of_mem ?_ hx
+      intro y hy
+      simpa [e] using e.right_inv (by simpa [e] using hy)
+    have hiff :
+        ChartedSpace.LiftPropWithinAt (ContDiffWithinAtProp I I 1) (Subtype.val ∘ e.symm)
+            (U : Set M) x ↔
+          ChartedSpace.LiftPropWithinAt (ContDiffWithinAtProp I I 1) e.symm (U : Set M) x :=
+      ChartedSpace.liftPropWithinAt_subtypeVal_comp_iff e.symm (U : Set M) x
+    simpa [ContMDiffWithinAt] using
+      hiff.mp (by simpa [ContMDiffWithinAt] using hcomp)
+  let Φ : PartialDiffeomorph I I U M 1 := {
+    toPartialEquiv := e.toPartialEquiv
+    open_source := e.open_source
+    open_target := e.open_target
+    contMDiffOn_toFun := by
+      simpa [e] using
+        ((contMDiff_subtype_val : ContMDiff I I 1 (Subtype.val : U → M)).contMDiffOn :
+          ContMDiffOn I I 1 (Subtype.val : U → M) Set.univ)
+    contMDiffOn_invFun := by
+      simpa [e] using hsymm }
+  have hp : p ∈ Φ.source := by
+    simp [Φ, e]
+  have hlocal : IsLocalDiffeomorphAt I I 1 (Φ : U → M) p := by
+    exact ⟨Φ, hp, fun x _ ↦ rfl⟩
+  have hinv : (mfderiv I I (Φ : U → M) p).IsInvertible := by
+    rw [← hlocal.mfderivToContinuousLinearEquiv_coe one_ne_zero]
+    exact ContinuousLinearMap.isInvertible_equiv
+  simpa [Φ, e] using hinv
+
+end OpenSubsetInclusion
+
+end Manifold