-- Mathlib/NumberTheory/NumberField/Embeddings.lean
theorem _root_.NumberField.is_primitive_element_of_infinitePlace_lt {x : 𝓞 K}
    {w : InfinitePlace K} (h₁ : x ≠ 0) (h₂ : ∀ ⦃w'⦄, w' ≠ w → w' x < 1)
    (h₃ : IsReal w ∨ |(w.embedding x).re| < 1) : ℚ⟮(x : K)⟯ = ⊤

Proof state:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
⊢ w = mk ψ.toRingHom

Tactic:
erw [← norm_embedding_eq, hψ] at h

Result:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ ‖ψ ↑x‖
⊢ w = mk ψ.toRingHom

Proof state:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
⊢ ℚ⟮↑x⟯ = ⊤

Tactic:
rw [Field.primitive_element_iff_algHom_eq_of_eval ℚ ℂ ?_ _ w.embedding.toRatAlgHom]

Result:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
⊢ ∀ (ψ : K →ₐ[ℚ] ℂ), w.embedding.toRatAlgHom ↑x = ψ ↑x → w.embedding.toRatAlgHom = ψ

K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
⊢ ∀ (x : K), Polynomial.Splits (algebraMap ℚ ℂ) (minpoly ℚ x)

Proof state:
case inr
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
main : w.embedding = ψ.toRingHom ∨ ComplexEmbedding.conjugate w.embedding = ψ.toRingHom
hw : |(w.embedding ↑x).re| < 1
⊢ w.embedding.toRatAlgHom = ψ

Tactic:
refine congr_arg RingHom.toRatAlgHom (main.resolve_right fun h' ↦ hw.not_le ?_)

Result:
case inr
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
main : w.embedding = ψ.toRingHom ∨ ComplexEmbedding.conjugate w.embedding = ψ.toRingHom
hw : |(w.embedding ↑x).re| < 1
h' : ComplexEmbedding.conjugate w.embedding = ψ.toRingHom
⊢ 1 ≤ |(w.embedding ↑x).re|

Proof state:
case inr
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
main : w.embedding = ψ.toRingHom ∨ ComplexEmbedding.conjugate w.embedding = ψ.toRingHom
hw : |(w.embedding ↑x).re| < 1
h' : ComplexEmbedding.conjugate w.embedding = ψ.toRingHom
this : (w.embedding ↑x).im = 0
⊢ 1 ≤ |(w.embedding ↑x).re|

Tactic:
rwa [← norm_embedding_eq, ← Complex.re_add_im (embedding w x), this, Complex.ofReal_zero,
  zero_mul, add_zero, Complex.norm_real] at h

Result:
no goals

Proof state:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
⊢ w.embedding.toRatAlgHom = ψ

Tactic:
have main : w = InfinitePlace.mk ψ.toRingHom := by
  erw [← norm_embedding_eq, hψ] at h
  contrapose! h
  exact h₂ h.symm

Result:
K : Type u_2
inst✝¹ : Field K
inst✝ : NumberField K
x : 𝓞 K
w : InfinitePlace K
h₁ : x ≠ 0
h₂ : ∀ ⦃w' : InfinitePlace K⦄, w' ≠ w → w' ↑x < 1
h₃ : w.IsReal ∨ |(w.embedding ↑x).re| < 1
ψ : K →ₐ[ℚ] ℂ
hψ : w.embedding.toRatAlgHom ↑x = ψ ↑x
h : 1 ≤ w ↑x
main : w = mk ψ.toRingHom
⊢ w.embedding.toRatAlgHom = ψ