OAI/MathematicalPhysics/Elasticity/Planar.lean

GitHub source file

135 declarations, 0 contain sorry, 0 declared as axioms

  1. theorem OAI.ElasticityRegularity.exists_smooth_lp_multiplier line 16

    Source documentation

    A joint smooth compactly spatially supported coefficient yields a genuinely operator-norm-smooth family of actual L2 multipliers.

    theorem exists_smooth_lp_multiplier {S : Set E} (hS : IsCompact S)
        (a : P × E → ℂ) (ha : ContDiff ℝ (⊤ : ℕ∞) a)
        (hs : ∀ p x, x∉S → a (p,x)=0) :
        ∃ M : P → Lp ℂ 2 (volume : Measure E) →L[ℂ] Lp ℂ 2 (volume : Measure E),
          ContDiff ℝ (⊤ : ℕ∞) M ∧ ∀ p f,
            (M p f : 𝓢'(E,ℂ))=smulLeftCLM ℂ (fun x => a (p,x)) (f : 𝓢'(E,ℂ)) := by
    …
  2. def OAI.ElasticityPlanar.testSubmodule line 49
  3. abbrev OAI.ElasticityPlanar.Test line 66
  4. instance OAI.ElasticityPlanar.(instance at line 68) line 68
  5. lemma OAI.ElasticityPlanar.smooth line 70
  6. lemma OAI.ElasticityPlanar.compact line 71
  7. def OAI.ElasticityPlanar.d line 73
  8. lemma OAI.ElasticityPlanar.d_apply line 90
  9. def OAI.ElasticityPlanar.mulSmooth line 93
  10. def OAI.ElasticityPlanar.Z line 105
  11. def OAI.ElasticityPlanar.Zbar line 106
  12. lemma OAI.ElasticityPlanar.Z_apply line 108
  13. lemma OAI.ElasticityPlanar.Zbar_apply line 109
  14. lemma OAI.ElasticityPlanar.d_Z line 111
  15. lemma OAI.ElasticityPlanar.deriv_conj line 119
  16. lemma OAI.ElasticityPlanar.d_Zbar line 125
  17. lemma OAI.ElasticityPlanar.d_d line 134
  18. lemma OAI.ElasticityPlanar.d_comm line 142
  19. def OAI.ElasticityPlanar.pair line 150
  20. lemma OAI.ElasticityPlanar.integrable_pair line 152
  21. lemma OAI.ElasticityPlanar.pair_add_right line 155
  22. lemma OAI.ElasticityPlanar.pair_add_left line 159
  23. lemma OAI.ElasticityPlanar.pair_sub_right line 163
  24. lemma OAI.ElasticityPlanar.pair_sub_left line 167
  25. lemma OAI.ElasticityPlanar.pair_smul_right line 171
  26. lemma OAI.ElasticityPlanar.pair_smul_left line 176
  27. lemma OAI.ElasticityPlanar.pair_d line 181

    Source documentation

    Coordinate derivatives are skew adjoint on the actual test space.

    lemma pair_d (f g : Test) (v : ℂ) : pair f (d v g) = -pair (d v f) g := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.pair, OAI.ElasticityPlanar.d

  28. lemma OAI.ElasticityPlanar.pair_Z line 191
  29. lemma OAI.ElasticityPlanar.pair_Zbar line 196
  30. def OAI.ElasticityPlanar.B line 202

    Source documentation

    Twice dbar conjugated by exp(t|z|²/2).

    def B (t : ℝ) : Test →ₗ[ℂ] Test := d 1 + Complex.I • d Complex.I - (t : ℂ) • Z

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d, OAI.ElasticityPlanar.Z

  31. def OAI.ElasticityPlanar.C line 204

    Source documentation

    Formal Hermitian adjoint.

    def C (t : ℝ) : Test →ₗ[ℂ] Test := -d 1 + Complex.I • d Complex.I - (t : ℂ) • Zbar

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d, OAI.ElasticityPlanar.Zbar

  32. lemma OAI.ElasticityPlanar.pair_B line 206
  33. lemma OAI.ElasticityPlanar.pair_C line 214
  34. lemma OAI.ElasticityPlanar.Z_Zbar line 221
  35. lemma OAI.ElasticityPlanar.commutator line 228

    Source documentation

    Positive commutator of the two Gaussian-conjugated planar operators.

    lemma commutator (t : ℝ) (f : Test) :
        C t (B t f) - B t (C t f) = (4 * (t : ℂ)) • f := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.C, OAI.ElasticityPlanar.B

  36. lemma OAI.ElasticityPlanar.energy_identity line 240
  37. def OAI.ElasticityPlanar.mass line 248
  38. lemma OAI.ElasticityPlanar.mass_integral line 250
  39. lemma OAI.ElasticityPlanar.integrable_normSq line 255
  40. lemma OAI.ElasticityPlanar.mass_nonneg line 260
  41. lemma OAI.ElasticityPlanar.mass_eq_zero line 264
  42. theorem OAI.ElasticityPlanar.gaussian_coercivity line 275

    Source documentation

    An actual weighted support estimate, independent of any frame existence.

    theorem gaussian_coercivity (t : ℝ) (f : Test) :
        4 * t * mass f ≤ mass (B t f) := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.mass, OAI.ElasticityPlanar.B

  43. def OAI.ElasticityPlanar.gaussian line 283
  44. lemma OAI.ElasticityPlanar.smooth_gaussian line 286
  45. def OAI.ElasticityPlanar.W line 289
  46. lemma OAI.ElasticityPlanar.W_apply line 291
  47. lemma OAI.ElasticityPlanar.gaussian_ne_zero line 294
  48. lemma OAI.ElasticityPlanar.fderiv_gaussian line 296
  49. lemma OAI.ElasticityPlanar.d_W line 309
  50. lemma OAI.ElasticityPlanar.gaussian_conjugation line 323

    Source documentation

    Exact Gaussian conjugation of twice the planar Cauchy--Riemann operator.

    lemma gaussian_conjugation (t : ℝ) (f : Test) :
        B t (W t f) = W t (d 1 f + I • d I f) := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.B, OAI.ElasticityPlanar.W, OAI.ElasticityPlanar.d

  51. lemma OAI.ElasticityPlanar.normSq_sum_mul line 338
  52. lemma OAI.ElasticityPlanar.mass_bound line 347
  53. theorem OAI.ElasticityPlanar.compact_kernel_of_bound line 361

    Source documentation

    Compact-kernel uniqueness with a coefficient bound only where a column is nonzero. This is a genuine analytic theorem, not an assumed continuation rule.

    theorem compact_kernel_of_bound {n : Type*} [Fintype n]
        (a : n → n → ℂ → ℂ) (u : n → Test) (K : ℝ)
        (hb : ∀ z : ℂ, (∃ j, u j z ≠ 0) → ∀ i,
          (∑ j, Complex.normSq (a i j z)) ≤ K)
        (heq : ∀ i (z : ℂ),
          (d 1 (u i) + I • d I (u i) : Test) z = ∑ j, a i j z * u j z) :
        ∀ i, u i = 0 := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d

  54. theorem OAI.ElasticityPlanar.compact_kernel line 431

    Source documentation

    A smooth compactly supported solution of a planar matrix Cauchy--Riemann system with continuous coefficients is zero. No smallness is imposed.

    theorem compact_kernel {n : Type*} [Fintype n]
        (a : n → n → ℂ → ℂ) (ha : ∀ i j, Continuous (a i j))
        (u : n → Test)
        (heq : ∀ i (z : ℂ),
          (d 1 (u i) + I • d I (u i) : Test) z = ∑ j, a i j z * u j z) :
        ∀ i, u i = 0 := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d

  55. lemma OAI.ElasticityPlanar.normSq_add_le line 464
  56. lemma OAI.ElasticityPlanar.mass_add_le line 470
  57. lemma OAI.ElasticityPlanar.mass_mul_bound line 480
  58. lemma OAI.ElasticityPlanar.mass_smul line 484
  59. lemma OAI.ElasticityPlanar.pair_derivative_cross line 489
  60. lemma OAI.ElasticityPlanar.dbar_energy line 496

    Source documentation

    The exact two-dimensional elliptic energy identity for the actual dbar operator.

    lemma dbar_energy (f : Test) :
        mass (d 1 f + I • d I f)=mass (d 1 f)+mass (d I f) := by
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.mass, OAI.ElasticityPlanar.d

  61. theorem OAI.ElasticityPlanar.weighted_inhomogeneous_bound line 510

    Source documentation

    Quantitative Gaussian absorption for a system with no smallness of coefficients.

    theorem weighted_inhomogeneous_bound {n : Type*} [Fintype n]
        (a : n → n → ℂ → ℂ) (u v : n → Test) (K : ℝ) (hK : 0 ≤ K)
        (hb : ∀ z, (∃ j, u j z ≠ 0) → ∀ i, (∑ j, normSq (a i j z)) ≤ K)
        (heq : ∀ i z, (d 1 (u i)+I • d I (u i) : Test) z =
          v i z+∑ j, a i j z*u j z) :
        let t := (Fintype.card n : ℝ)*K+1
    …

    Mentions: OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d

  62. lemma OAI.ElasticityPlanar.gaussian_inv line 568
  63. lemma OAI.ElasticityPlanar.supported_weight_bound line 575
  64. lemma OAI.ElasticityPlanar.supported_weight_equivalence line 592
  65. lemma OAI.ElasticityPlanar.matrix_bound_on_compact line 613
  66. theorem OAI.ElasticityPlanar.supported_inhomogeneous_L2 line 631

    Source documentation

    A true unweighted supported L2 estimate, uniform over all test columns on a fixed compact set, for an arbitrary continuous matrix coefficient.

    theorem supported_inhomogeneous_L2 {n : Type*} [Fintype n]
        {S : Set ℂ} (hS : IsCompact S) (a : n → n → ℂ → ℂ)
        (ha : ∀ i j, Continuous (a i j)) :
        ∃ C : ℝ, 0<C ∧ ∀ u v : n → Test,
          (∀ i, tsupport (u i : ℂ → ℂ) ⊆ S) →
          (∀ i, tsupport (v i : ℂ → ℂ) ⊆ S) →
          (∀ i z, (d 1 (u i)+I • d I (u i) : Test) z=v i z+∑ j, a i j z*u j z) →
          (∑ i, mass (u i)) ≤ C*∑ i, mass (v i) := by
    …

    Mentions: OAI.ElasticityPlanar.C, OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.d, OAI.ElasticityPlanar.mass

  67. lemma OAI.ElasticityDualSolvability.weak_unique_in_range line 665
  68. theorem OAI.ElasticityDualSolvability.exists_linear_weak_solver line 679

    Source documentation

    Hilbert projection makes the actual Hahn--Banach solver canonical and linear. It will be used for smooth parameter dependence of the planar right inverse.

    theorem exists_linear_weak_solver (D : Submodule ℂ H) (A : D →ₗ[ℂ] H)
        (C : ℝ) (hC : 0 ≤ C) (hA : ∀ v : D, ‖(v : H)‖ ≤ C*‖A v‖) :
        ∃ T : H →L[ℂ] H, ‖T‖ ≤ C ∧ ∀ f v, inner ℂ (T f) (A v)=inner ℂ f (v : H) := by
    …
  69. def OAI.ElasticityPlanar.toSchwartz line 713
  70. lemma OAI.ElasticityPlanar.toSchwartz_apply line 717
  71. lemma OAI.ElasticityPlanar.toSchwartz_injective line 718
  72. def OAI.ElasticityPlanar.L2 line 723
  73. lemma OAI.ElasticityPlanar.L2_injective line 725
  74. lemma OAI.ElasticityPlanar.inner_L2 line 726
  75. lemma OAI.ElasticityPlanar.norm_L2_sq line 730
  76. def OAI.ElasticityPlanar.cj line 734
  77. lemma OAI.ElasticityPlanar.cj_apply line 736
  78. lemma OAI.ElasticityPlanar.cj_cj line 737
  79. lemma OAI.ElasticityPlanar.cj_d line 738
  80. lemma OAI.ElasticityPlanar.cj_add line 742
  81. lemma OAI.ElasticityPlanar.cj_neg line 743
  82. lemma OAI.ElasticityPlanar.cj_smul line 744
  83. lemma OAI.ElasticityPlanar.mass_cj line 749
  84. lemma OAI.ElasticityPlanar.support_cj line 754
  85. abbrev OAI.ElasticityPlanar.Hilbert line 761
  86. def OAI.ElasticityPlanar.embed line 762
  87. lemma OAI.ElasticityPlanar.embed_apply line 766
  88. lemma OAI.ElasticityPlanar.embed_injective line 767
  89. lemma OAI.ElasticityPlanar.norm_embed_sq line 772
  90. lemma OAI.ElasticityPlanar.norm_embed_cj line 775
  91. def OAI.ElasticityPlanar.transport line 781

    Source documentation

    Actual first-order matrix transport on compactly supported smooth tests.

    def transport (a : n → n → ℂ → ℂ) (ha : ∀ i j, ContDiff ℝ (⊤ : ℕ∞) (a i j)) :
        (n → Test) →ₗ[ℂ] (n → Test) where
    …

    Mentions: OAI.ElasticityPlanar.Test

  92. lemma OAI.ElasticityPlanar.transport_supported line 792
  93. theorem OAI.ElasticityPlanar.supported_transport_estimate line 813

    Source documentation

    A true L2 lower bound for the actual transport operator.

    theorem supported_transport_estimate {S : Set ℂ} (hS : IsCompact S)
        (a : n → n → ℂ → ℂ) (ha : ∀ i j, ContDiff ℝ (⊤ : ℕ∞) (a i j)) :
        ∃ C : ℝ, 0<C ∧ ∀ u : n → Test, (∀ i, tsupport (u i : ℂ → ℂ) ⊆ S) →
          ‖embed u‖ ≤ C*‖embed (transport a ha u)‖ := by
    …

    Mentions: OAI.ElasticityPlanar.C, OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.embed, OAI.ElasticityPlanar.transport

  94. def OAI.ElasticityPlanar.adjTransport line 839

    Source documentation

    The genuine Hermitian formal adjoint of dbar+a, written using conjugation and the transpose coefficient. No elliptic right inverse is assumed.

    def adjTransport (a : n → n → ℂ → ℂ) (ha : ∀ i j, ContDiff ℝ (⊤ : ℕ∞) (a i j)) :
        (n → Test) →ₗ[ℂ] (n → Test) where
    …

    Mentions: OAI.ElasticityPlanar.Test

  95. lemma OAI.ElasticityPlanar.norm_adjTransport line 856
  96. def OAI.ElasticityPlanar.supported line 863

    Source documentation

    Supported test vectors form the actual L2 domain for the adjoint.

    def supported (S : Set ℂ) : Submodule ℂ (n → Test) where
    …

    Mentions: OAI.ElasticityPlanar.Test

  97. theorem OAI.ElasticityPlanar.exists_planar_weak_inverse line 872

    Source documentation

    Actual supported matrix transport has a bounded linear L2 weak right inverse. The estimate comes from the proved Gaussian positive commutator, not a smallness assumption or a globally given frame.

    theorem exists_planar_weak_inverse {S : Set ℂ} (hS : IsCompact S)
        (a : n → n → ℂ → ℂ) (ha : ∀ i j, ContDiff ℝ (⊤ : ℕ∞) (a i j)) :
        ∃ C : ℝ, 0<C ∧ ∃ T : Hilbert n →L[ℂ] Hilbert n, ‖T‖ ≤ C ∧
          ∀ f : Hilbert n, ∀ u : n → Test, (∀ i, tsupport (u i : ℂ → ℂ) ⊆ S) →
            inner ℂ (T f) (embed (adjTransport a ha u))=inner ℂ f (embed u) := by
    …

    Mentions: OAI.ElasticityPlanar.C, OAI.ElasticityPlanar.Hilbert, OAI.ElasticityPlanar.Test, OAI.ElasticityPlanar.embed, OAI.ElasticityPlanar.adjTransport

  98. abbrev OAI.ElasticityPlanarDistribution.Test line 906
  99. abbrev OAI.ElasticityPlanarDistribution.Dist line 907
  100. def OAI.ElasticityPlanarDistribution.dbar line 908
  101. def OAI.ElasticityPlanarDistribution.dhol line 909
  102. lemma OAI.ElasticityPlanarDistribution.schwartz_derivative_commute line 911
  103. lemma OAI.ElasticityPlanarDistribution.derivative_commute line 923
  104. lemma OAI.ElasticityPlanarDistribution.dhol_dbar line 928
  105. lemma OAI.ElasticityPlanarDistribution.dhol_sum line 935
  106. lemma OAI.ElasticityPlanarDistribution.dhol_add line 938
  107. lemma OAI.ElasticityPlanarDistribution.LocalEqual.dhol line 941
  108. lemma OAI.ElasticityPlanarDistribution.LocalSobolev.dhol line 944
  109. def OAI.ElasticityPlanarDistribution.Equation line 950

    Source documentation

    Actual planar first-order equation on distributions, not an abstract regularity or frame existence interface.

    def Equation {n : Type*} [Fintype n] (Ω : Set ℂ) (a : n → n → ℂ → ℂ) (u f : n → Dist) : Prop :=
    …

    Mentions: OAI.ElasticityPlanarDistribution.Dist

  110. theorem OAI.ElasticityPlanarDistribution.local_gain line 953
  111. theorem OAI.ElasticityPlanarDistribution.local_all_orders line 967
  112. theorem OAI.ElasticityPlanarDistribution.cutoff_smooth line 980
  113. lemma OAI.ElasticityPlanar.toSchwartz_d line 996
  114. lemma OAI.ElasticityPlanar.toSchwartz_mul line 999
  115. lemma OAI.ElasticityPlanar.Lp_test line 1004
  116. lemma OAI.ElasticityPlanar.vector_transpose line 1014
  117. lemma OAI.ElasticityPlanar.weak_to_vector_distribution line 1034
  118. lemma OAI.ElasticityPlanar.weak_to_local_equation line 1053
  119. theorem OAI.ElasticityRegularity.exists_continuous_lift line 1079

    Source documentation

    The closed graph argument supplies norms for genuine distribution operators, not additional quantitative regularity assumptions.

    theorem exists_continuous_lift
        {X Y Z : Type*} [NormedAddCommGroup X] [NormedSpace ℂ X] [CompleteSpace X]
        [NormedAddCommGroup Y] [NormedSpace ℂ Y] [CompleteSpace Y]
        [AddCommGroup Z] [Module ℂ Z] [TopologicalSpace Z] [T2Space Z]
        (J : Y →L[ℂ] Z) (hJ : Function.Injective J) (T : X →L[ℂ] Z)
        (hT : ∀ x, ∃ y, J y=T x) :
        ∃ L : X →L[ℂ] Y, ∀ x, J (L x)=T x := by
    …
  120. lemma OAI.ElasticityRegularity.lp_distribution_injective line 1109
  121. def OAI.ElasticityRegularity.sobolevInjection line 1120

    Source documentation

    H^s is represented isometrically by L2 via J^{-s}; its injection is into the actual space of tempered distributions.

    def sobolevInjection (s : ℝ) : Lp ℂ 2 (volume : Measure E) →L[ℂ] 𝓢'(E,ℂ) :=
    …
  122. lemma OAI.ElasticityRegularity.sobolevInjection_injective line 1123
  123. lemma OAI.ElasticityRegularity.sobolevInjection_mem line 1133
  124. lemma OAI.ElasticityRegularity.memSobolev_iff_range line 1140
  125. theorem OAI.ElasticityRegularity.exists_sobolev_realization line 1153

    Source documentation

    A qualitative everywhere-defined Sobolev mapping theorem for a continuous actual distribution operator automatically gives its bounded Sobolev realization. This is useful for smooth multipliers and coordinate derivatives on cutoffs.

    theorem exists_sobolev_realization (s t : ℝ) (P : 𝓢'(E,ℂ) →L[ℂ] 𝓢'(E,ℂ))
        (hP : ∀ u, MemSobolev s 2 u → MemSobolev t 2 (P u)) :
        ∃ L : Lp ℂ 2 (volume : Measure E) →L[ℂ] Lp ℂ 2 (volume : Measure E),
          ∀ f, sobolevInjection t (L f)=P (sobolevInjection s f) := by
    …

    Mentions: OAI.ElasticityRegularity.sobolevInjection

  126. theorem OAI.ElasticityRegularity.exists_bounded_sobolev_derivative line 1161
  127. theorem OAI.ElasticityRegularity.exists_bounded_sobolev_inclusion line 1167
  128. theorem OAI.ElasticityRegularity.sobolev_neg_one_product line 1184

    Source documentation

    Compact smooth multiplication on the negative initial Sobolev order in which the physical divergence is initially controlled.

    theorem sobolev_neg_one_product {g : E → ℂ}
        (hg : ContDiff ℝ (⊤ : ℕ∞) g) (hc : HasCompactSupport g)
        {u : 𝓢'(E,ℂ)} (hu : MemSobolev (-1) 2 u) :
        MemSobolev (-1) 2 (smulLeftCLM ℂ g u) := by
    …
  129. lemma OAI.ElasticityRegularity.sobolev_product_step_down line 1213
  130. theorem OAI.ElasticityRegularity.sobolev_negative_product line 1252

    Source documentation

    Smooth compact multiplication preserves every integral Sobolev order, including the H^-2 forcing order in the first augmented bootstrap step.

    theorem sobolev_negative_product (n : ℕ) {g : E → ℂ}
        (hg : ContDiff ℝ (⊤ : ℕ∞) g) (hc : HasCompactSupport g)
        {u : 𝓢'(E,ℂ)} (hu : MemSobolev (-(n : ℝ)) 2 u) :
        MemSobolev (-(n : ℝ)) 2 (smulLeftCLM ℂ g u) := by
    …
  131. theorem OAI.ElasticityRegularity.exists_bounded_negative_multiplier line 1267
  132. theorem OAI.ElasticityRegularity.exists_bounded_nat_multiplier line 1274
  133. theorem OAI.ElasticityDualSolvability.perturbed_weak_solver line 1285

    Source documentation

    A bounded zeroth-order perturbation of an actual weak right inverse.

    theorem perturbed_weak_solver (D : Submodule ℂ H) (A : D →ₗ[ℂ] H)
        (T B Q : H →L[ℂ] H)
        (hT : ∀ f v, inner ℂ (T f) (A v)=inner ℂ f (v : H))
        (hQ : (1+B*T)*Q=1) (f : H) (v : D) :
        inner ℂ ((T*Q) f) (A v+B.adjoint (v : H))=inner ℂ f (v : H) := by
    …
  134. theorem OAI.ElasticityDualSolvability.perturbed_weak_inverse line 1298

    Source documentation

    The perturbative solver exists without adding a range surjectivity assumption. The smallness condition is strictly local in parameter space.

    theorem perturbed_weak_inverse (D : Submodule ℂ H) (A : D →ₗ[ℂ] H)
        (T B : H →L[ℂ] H)
        (hT : ∀ f v, inner ℂ (T f) (A v)=inner ℂ f (v : H))
        (hBT : ‖B*T‖<1) :
        ∀ f v, inner ℂ ((T*Ring.inverse (1+B*T)) f) (A v+B.adjoint (v : H))=
          inner ℂ f (v : H) := by
    …
  135. theorem OAI.ElasticityDualSolvability.smooth_local_weak_inverse line 1311

    Source documentation

    Smooth dependence of the local Neumann inverse, established with the stock Banach-algebra inversion theorem.

    theorem smooth_local_weak_inverse {P : Type*} [NormedAddCommGroup P] [NormedSpace ℝ P]
        (T : H →L[ℂ] H) (B : P → H →L[ℂ] H) {p : P}
        (hB : ContDiffAt ℝ (⊤ : ℕ∞) B p) (hBT : ‖B p*T‖<1) :
        ContDiffAt ℝ (⊤ : ℕ∞) (fun q => T*Ring.inverse (1+B q*T)) p := by
    …