Theorem: NumberField.exists_ne_zero_mem_ideal_of_norm_le_mul_sqrt_discr
File: Mathlib/NumberTheory/NumberField/Discriminant.lean

Proof steps:
state_before: K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      ↑|(Algebra.norm ℚ) a| ≤
        ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial /
            ↑(finrank ℚ K) ^ finrank ℚ K *
          √|↑(discr K)|
state_after: K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      ↑|(Algebra.norm ℚ) a| ≤
        ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial /
            ↑(finrank ℚ K) ^ finrank ℚ K *
          √|↑(discr K)|
tactic: let B := (minkowskiBound K I * (convexBodySumFactor K)⁻¹).toReal ^ (1 / (finrank ℚ K : ℝ))
state_before: K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
⊢ ∃ a ∈ ↑I,
    a ≠ 0 ∧
      ↑|(Algebra.norm ℚ) a| ≤
        ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial /
            ↑(finrank ℚ K) ^ finrank ℚ K *
          √|↑(discr K)|
state_after: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial /
        ↑(finrank ℚ K) ^ finrank ℚ K *
      √|↑(discr K)| =
    (B / ↑(finrank ℚ K)) ^ finrank ℚ K
tactic: convert exists_ne_zero_mem_ideal_of_norm_le K I h_le
state_before: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial /
        ↑(finrank ℚ K) ^ finrank ℚ K *
      √|↑(discr K)| =
    (B / ↑(finrank ℚ K)) ^ finrank ℚ K
state_after: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)| /
      ↑(finrank ℚ K) ^ finrank ℚ K =
    (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal / ↑(finrank ℚ K) ^ finrank ℚ K
tactic: rw [div_pow B, ← Real.rpow_natCast B, ← Real.rpow_mul (by positivity), div_mul_cancel₀ _
    (Nat.cast_ne_zero.mpr <| ne_of_gt finrank_pos), Real.rpow_one, mul_comm_div, mul_div_assoc']
state_before: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)| /
      ↑(finrank ℚ K) ^ finrank ℚ K =
    (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal / ↑(finrank ℚ K) ^ finrank ℚ K
state_after: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4.e_a
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)| =
    (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal
tactic: congr 1
state_before: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4.e_a
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)| =
    (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal
state_after: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4.e_a
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal =
    ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)|
tactic: rw [eq_comm]
state_before: case h.e'_2.h.h.e'_2.h.e'_2.h.e'_4.e_a
K : Type u_1
inst✝¹ : Field K
inst✝ : NumberField K
I : (FractionalIdeal (𝓞 K)⁰ K)ˣ
B : ℝ := (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal ^ (1 / ↑(finrank ℚ K))
h_le : minkowskiBound K I ≤ volume (convexBodySum K B)
x✝ : K
⊢ (minkowskiBound K I * ↑(convexBodySumFactor K)⁻¹).toReal =
    ↑(FractionalIdeal.absNorm ↑I) * (4 / π) ^ NrComplexPlaces K * ↑(finrank ℚ K).factorial * √|↑(discr K)|
state_after: no goals
tactic: calc
    _ = FractionalIdeal.absNorm I.1 * (2 : ℝ)⁻¹ ^ NrComplexPlaces K * sqrt ‖discr K‖₊ *
          (2 : ℝ) ^ finrank ℚ K * ((2 : ℝ) ^ NrRealPlaces K * (π / 2) ^ NrComplexPlaces K /
            (Nat.factorial (finrank ℚ K)))⁻¹ := by
      simp_rw [minkowskiBound, convexBodySumFactor,
        volume_fundamentalDomain_fractionalIdealLatticeBasis,
        volume_fundamentalDomain_latticeBasis, toReal_mul, toReal_pow, toReal_inv, coe_toReal,
        toReal_ofNat, mixedEmbedding.finrank, mul_assoc]
      rw [ENNReal.toReal_ofReal (Rat.cast_nonneg.mpr (FractionalIdeal.absNorm_nonneg I.1))]
      simp_rw [NNReal.coe_inv, NNReal.coe_div, NNReal.coe_mul, NNReal.coe_pow, NNReal.coe_div,
        coe_real_pi, NNReal.coe_ofNat, NNReal.coe_natCast]
    _ = FractionalIdeal.absNorm I.1 * (2 : ℝ) ^ (finrank ℚ K - NrComplexPlaces K - NrRealPlaces K +
          NrComplexPlaces K : ℤ) * Real.sqrt ‖discr K‖ * Nat.factorial (finrank ℚ K) *
            π⁻¹ ^ (NrComplexPlaces K) := by
      simp_rw [inv_div, div_eq_mul_inv, mul_inv, ← zpow_neg_one, ← zpow_natCast, mul_zpow,
        ← zpow_mul, neg_one_mul, mul_neg_one, neg_neg, Real.coe_sqrt, coe_nnnorm, sub_eq_add_neg,
        zpow_add₀ (two_ne_zero : (2 : ℝ) ≠ 0)]
      ring
    _ = FractionalIdeal.absNorm I.1 * (2 : ℝ) ^ (2 * NrComplexPlaces K : ℤ) * Real.sqrt ‖discr K‖ *
          Nat.factorial (finrank ℚ K) * π⁻¹ ^ (NrComplexPlaces K) := by
      congr
      rw [← card_add_two_mul_card_eq_rank, Nat.cast_add, Nat.cast_mul, Nat.cast_ofNat]
      ring
    _ = FractionalIdeal.absNorm I.1 * (4 / π) ^ NrComplexPlaces K * (finrank ℚ K).factorial *
          Real.sqrt |discr K| := by
      rw [Int.norm_eq_abs, zpow_mul, show (2 : ℝ) ^ (2 : ℤ) = 4 by norm_cast, div_pow,
        inv_eq_one_div, div_pow, one_pow, zpow_natCast]
      ring