-- Mathlib/NumberTheory/NumberField/CanonicalEmbedding/ConvexBody.lean
theorem exists_ne_zero_mem_ideal_lt' (w₀ : {w : InfinitePlace K // IsComplex w})
    (h : minkowskiBound K I < volume (convexBodyLT' K f w₀)) :
    ∃ a ∈ (I : FractionalIdeal (𝓞 K)⁰ K), a ≠ 0 ∧ (∀ w : InfinitePlace K, w ≠ w₀ → w a < f w) ∧
      |(w₀.val.embedding a).re| < 1 ∧ |(w₀.val.embedding a).im| < (f w₀ : ℝ) ^ 2

Proof state:
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
f : InfinitePlace K → ℝ≥0
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
w₀ : { w // w.IsComplex }
h : minkowskiBound K I < volume (convexBodyLT' K f w₀)
h_fund :
  IsAddFundamentalDomain (↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup)
    (fundamentalDomain (fractionalIdealLatticeBasis K I)) volume
this : Countable ↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      (∀ (w : InfinitePlace K), w ≠ ↑w₀ → w a < ↑(f w)) ∧
        |((↑w₀).embedding a).re| < 1 ∧ |((↑w₀).embedding a).im| < ↑(f ↑w₀) ^ 2

Tactic:
obtain ⟨⟨x, hx⟩, h_nz, h_mem⟩ := exists_ne_zero_mem_lattice_of_measure_mul_two_pow_lt_measure
  h_fund (convexBodyLT'_neg_mem K f w₀) (convexBodyLT'_convex K f w₀) h

Result:
case intro.mk.intro
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
f : InfinitePlace K → ℝ≥0
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
w₀ : { w // w.IsComplex }
h : minkowskiBound K I < volume (convexBodyLT' K f w₀)
h_fund :
  IsAddFundamentalDomain (↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup)
    (fundamentalDomain (fractionalIdealLatticeBasis K I)) volume
this : Countable ↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
x : mixedSpace K
hx : x ∈ (span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
h_nz : ⟨x, hx⟩ ≠ 0
h_mem : ↑⟨x, hx⟩ ∈ convexBodyLT' K f w₀
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      (∀ (w : InfinitePlace K), w ≠ ↑w₀ → w a < ↑(f w)) ∧
        |((↑w₀).embedding a).re| < 1 ∧ |((↑w₀).embedding a).im| < ↑(f ↑w₀) ^ 2

Proof state:
case intro.mk.intro
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
f : InfinitePlace K → ℝ≥0
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
w₀ : { w // w.IsComplex }
h : minkowskiBound K I < volume (convexBodyLT' K f w₀)
h_fund :
  IsAddFundamentalDomain (↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup)
    (fundamentalDomain (fractionalIdealLatticeBasis K I)) volume
this : Countable ↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
x : mixedSpace K
hx✝ : x ∈ (span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
hx : x ∈ ⇑(mixedEmbedding K) '' ↑↑I
h_nz : ⟨x, hx✝⟩ ≠ 0
h_mem : ↑⟨x, hx✝⟩ ∈ convexBodyLT' K f w₀
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      (∀ (w : InfinitePlace K), w ≠ ↑w₀ → w a < ↑(f w)) ∧
        |((↑w₀).embedding a).re| < 1 ∧ |((↑w₀).embedding a).im| < ↑(f ↑w₀) ^ 2

Tactic:
obtain ⟨a, ha, rfl⟩ := hx

Result:
case intro.mk.intro.intro.intro
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
f : InfinitePlace K → ℝ≥0
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
w₀ : { w // w.IsComplex }
h : minkowskiBound K I < volume (convexBodyLT' K f w₀)
h_fund :
  IsAddFundamentalDomain (↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup)
    (fundamentalDomain (fractionalIdealLatticeBasis K I)) volume
this : Countable ↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
a : K
ha : a ∈ ↑↑I
hx : (mixedEmbedding K) a ∈ (span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup
h_nz : ⟨(mixedEmbedding K) a, hx⟩ ≠ 0
h_mem : ↑⟨(mixedEmbedding K) a, hx⟩ ∈ convexBodyLT' K f w₀
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      (∀ (w : InfinitePlace K), w ≠ ↑w₀ → w a < ↑(f w)) ∧
        |((↑w₀).embedding a).re| < 1 ∧ |((↑w₀).embedding a).im| < ↑(f ↑w₀) ^ 2

Proof state:
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
f : InfinitePlace K → ℝ≥0
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
w₀ : { w // w.IsComplex }
h : minkowskiBound K I < volume (convexBodyLT' K f w₀)
h_fund :
  IsAddFundamentalDomain (↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I))).toAddSubgroup)
    (fundamentalDomain (fractionalIdealLatticeBasis K I)) volume
⊢ Countable ↥(span ℤ (Set.range ⇑(fractionalIdealLatticeBasis K I)))

Tactic:
infer_instance

Result:
no goals