Module: Mathlib.Analysis.Normed.Unbundled.FiniteExtension

Goal state before:
pp: K : Type u_1
L : Type u_2
inst✝² : NormedField K
inst✝¹ : Field L
inst✝ : Algebra K L
hfd : FiniteDimensional K L
hna : IsNonarchimedean norm
h1 : LinearIndepOn K id {1}
ι : Type u_2 := { x // x ∈ h1.extend ⋯ }
B : Basis ι K L := Basis.extend h1
hfin : Fintype ι := FiniteDimensional.fintypeBasisIndex B
hem : Nonempty ι
h1L : 1 ∈ h1.extend ⋯
hB1 : B ⟨1, h1L⟩ = 1
g : L → ℝ := B.norm
hg0 : g 0 = 0
hg_nonneg : ∀ (x : L), 0 ≤ g x
hg_ext : ∀ (x : K), g ((algebraMap K L) x) = ‖x‖
hg_na : IsNonarchimedean g
hg_add : ∀ (a b : L), g (a + b) ≤ g a + g b
hg_neg : ∀ (a : L), g (-a) = g a
w✝¹ : ℝ
w✝ : 0 < w✝¹
hg_bdd : ∀ (x y : L), B.norm (x * y) ≤ w✝¹ * B.norm x * B.norm y
hg_mul : ∀ (k : K) (y : L), g ((algebraMap K L) k * y) = g ((algebraMap K L) k) * g y
f : RingSeminorm L := seminormFromBounded hg0 hg_nonneg hg_bdd hg_add hg_neg
hf_na : IsNonarchimedean ⇑f
hf_1 : f 1 ≤ 1
hf_ext : ∀ (x : K), f ((algebraMap K L) x) = ‖x‖
F' : RingSeminorm L := smoothingSeminorm f hf_1 hf_na
hF' : F' = smoothingSeminorm f hf_1 hf_na
hF'_ext : ∀ (k : K), F' ((algebraMap K L) k) = ‖k‖
hF'_1 : F' 1 = 1
hF'_0 : F' ≠ 0
⊢ ∃ f, IsPowMul ⇑f ∧ (∀ (x : K), f ((algebraMap K L) x) = ‖x‖) ∧ IsNonarchimedean ⇑f

Tactic:
set F : AlgebraNorm K L :=
    { RingSeminorm.toRingNorm F' hF'_0 with
      smul' := fun k y ↦ by
        have hk : ∀ y : L, f (algebraMap K L k * y) = f (algebraMap K L k) * f y :=
          seminormFromBounded_of_mul_is_mul hg_nonneg hg_bdd (hg_mul k)
        have hfk : ‖k‖ = (smoothingSeminorm f hf_1 hf_na) ((algebraMap K L) k) := by
          rw [← hf_ext k, eq_comm, smoothingSeminorm_apply_of_map_mul_eq_mul f hf_1 hf_na hk]
        simp only [hfk, hF']
        -- TODO: There are missing `simp` lemmas here, that should be able to convert
        -- `((smoothingSeminorm f hf_1 hf_na).toRingNorm ⋯).toRingSeminorm y` to
        -- `(smoothingSeminorm f hf_1 hf_na y)`, after which the `erw` would work as a `rw`.
        erw [← smoothingSeminorm_of_mul f hf_1 hf_na hk y]
        rw [Algebra.smul_def]
        rfl }

Goal state after:
K : Type u_1
L : Type u_2
inst✝² : NormedField K
inst✝¹ : Field L
inst✝ : Algebra K L
hfd : FiniteDimensional K L
hna : IsNonarchimedean norm
h1 : LinearIndepOn K id {1}
ι : Type u_2 := { x // x ∈ h1.extend ⋯ }
B : Basis ι K L := Basis.extend h1
hfin : Fintype ι := FiniteDimensional.fintypeBasisIndex B
hem : Nonempty ι
h1L : 1 ∈ h1.extend ⋯
hB1 : B ⟨1, h1L⟩ = 1
g : L → ℝ := B.norm
hg0 : g 0 = 0
hg_nonneg : ∀ (x : L), 0 ≤ g x
hg_ext : ∀ (x : K), g ((algebraMap K L) x) = ‖x‖
hg_na : IsNonarchimedean g
hg_add : ∀ (a b : L), g (a + b) ≤ g a + g b
hg_neg : ∀ (a : L), g (-a) = g a
w✝¹ : ℝ
w✝ : 0 < w✝¹
hg_bdd : ∀ (x y : L), B.norm (x * y) ≤ w✝¹ * B.norm x * B.norm y
hg_mul : ∀ (k : K) (y : L), g ((algebraMap K L) k * y) = g ((algebraMap K L) k) * g y
f : RingSeminorm L := seminormFromBounded hg0 hg_nonneg hg_bdd hg_add hg_neg
hf_na : IsNonarchimedean ⇑f
hf_1 : f 1 ≤ 1
hf_ext : ∀ (x : K), f ((algebraMap K L) x) = ‖x‖
F' : RingSeminorm L := smoothingSeminorm f hf_1 hf_na
hF' : F' = smoothingSeminorm f hf_1 hf_na
hF'_ext : ∀ (k : K), F' ((algebraMap K L) k) = ‖k‖
hF'_1 : F' 1 = 1
hF'_0 : F' ≠ 0
F : AlgebraNorm K L :=
  let __src := F'.toRingNorm hF'_0;
  { toRingNorm := __src, smul' := ⋯ }
⊢ ∃ f, IsPowMul ⇑f ∧ (∀ (x : K), f ((algebraMap K L) x) = ‖x‖) ∧ IsNonarchimedean ⇑f