Theorem: ENNReal.lintegral_mul_le_Lp_mul_Lq_of_ne_zero_of_ne_top
File: Mathlib/MeasureTheory/Integral/MeanInequalities.lean

Proof steps:
state_before: α : Type u_1
inst✝ : MeasurableSpace α
μ : Measure α
p q : ℝ
hpq : p.IsConjExponent q
f g : α → ℝ≥0∞
hf : AEMeasurable f μ
hf_nontop : ∫⁻ (a : α), f a ^ p ∂μ ≠ ⊤
hg_nontop : ∫⁻ (a : α), g a ^ q ∂μ ≠ ⊤
hf_nonzero : ∫⁻ (a : α), f a ^ p ∂μ ≠ 0
hg_nonzero : ∫⁻ (a : α), g a ^ q ∂μ ≠ 0
⊢ ∫⁻ (a : α), (f * g) a ∂μ ≤ (∫⁻ (a : α), f a ^ p ∂μ) ^ (1 / p) * (∫⁻ (a : α), g a ^ q ∂μ) ^ (1 / q)
state_after: α : Type u_1
inst✝ : MeasurableSpace α
μ : Measure α
p q : ℝ
hpq : p.IsConjExponent q
f g : α → ℝ≥0∞
hf : AEMeasurable f μ
hf_nontop : ∫⁻ (a : α), f a ^ p ∂μ ≠ ⊤
hg_nontop : ∫⁻ (a : α), g a ^ q ∂μ ≠ ⊤
hf_nonzero : ∫⁻ (a : α), f a ^ p ∂μ ≠ 0
hg_nonzero : ∫⁻ (a : α), g a ^ q ∂μ ≠ 0
npf : ℝ≥0∞ := (∫⁻ (c : α), f c ^ p ∂μ) ^ (1 / p)
⊢ ∫⁻ (a : α), (f * g) a ∂μ ≤ (∫⁻ (a : α), f a ^ p ∂μ) ^ (1 / p) * (∫⁻ (a : α), g a ^ q ∂μ) ^ (1 / q)
tactic: let npf := (∫⁻ c : α, f c ^ p ∂μ) ^ (1 / p)
state_before: α : Type u_1
inst✝ : MeasurableSpace α
μ : Measure α
p q : ℝ
hpq : p.IsConjExponent q
f g : α → ℝ≥0∞
hf : AEMeasurable f μ
hf_nontop : ∫⁻ (a : α), f a ^ p ∂μ ≠ ⊤
hg_nontop : ∫⁻ (a : α), g a ^ q ∂μ ≠ ⊤
hf_nonzero : ∫⁻ (a : α), f a ^ p ∂μ ≠ 0
hg_nonzero : ∫⁻ (a : α), g a ^ q ∂μ ≠ 0
npf : ℝ≥0∞ := (∫⁻ (c : α), f c ^ p ∂μ) ^ (1 / p)
⊢ ∫⁻ (a : α), (f * g) a ∂μ ≤ (∫⁻ (a : α), f a ^ p ∂μ) ^ (1 / p) * (∫⁻ (a : α), g a ^ q ∂μ) ^ (1 / q)
state_after: α : Type u_1
inst✝ : MeasurableSpace α
μ : Measure α
p q : ℝ
hpq : p.IsConjExponent q
f g : α → ℝ≥0∞
hf : AEMeasurable f μ
hf_nontop : ∫⁻ (a : α), f a ^ p ∂μ ≠ ⊤
hg_nontop : ∫⁻ (a : α), g a ^ q ∂μ ≠ ⊤
hf_nonzero : ∫⁻ (a : α), f a ^ p ∂μ ≠ 0
hg_nonzero : ∫⁻ (a : α), g a ^ q ∂μ ≠ 0
npf : ℝ≥0∞ := (∫⁻ (c : α), f c ^ p ∂μ) ^ (1 / p)
nqg : ℝ≥0∞ := (∫⁻ (c : α), g c ^ q ∂μ) ^ (1 / q)
⊢ ∫⁻ (a : α), (f * g) a ∂μ ≤ (∫⁻ (a : α), f a ^ p ∂μ) ^ (1 / p) * (∫⁻ (a : α), g a ^ q ∂μ) ^ (1 / q)
tactic: let nqg := (∫⁻ c : α, g c ^ q ∂μ) ^ (1 / q)
state_before: α : Type u_1
inst✝ : MeasurableSpace α
μ : Measure α
p q : ℝ
hpq : p.IsConjExponent q
f g : α → ℝ≥0∞
hf : AEMeasurable f μ
hf_nontop : ∫⁻ (a : α), f a ^ p ∂μ ≠ ⊤
hg_nontop : ∫⁻ (a : α), g a ^ q ∂μ ≠ ⊤
hf_nonzero : ∫⁻ (a : α), f a ^ p ∂μ ≠ 0
hg_nonzero : ∫⁻ (a : α), g a ^ q ∂μ ≠ 0
npf : ℝ≥0∞ := (∫⁻ (c : α), f c ^ p ∂μ) ^ (1 / p)
nqg : ℝ≥0∞ := (∫⁻ (c : α), g c ^ q ∂μ) ^ (1 / q)
⊢ ∫⁻ (a : α), (f * g) a ∂μ ≤ (∫⁻ (a : α), f a ^ p ∂μ) ^ (1 / p) * (∫⁻ (a : α), g a ^ q ∂μ) ^ (1 / q)
state_after: no goals
tactic: calc
    (∫⁻ a : α, (f * g) a ∂μ) =
        ∫⁻ a : α, (funMulInvSnorm f p μ * funMulInvSnorm g q μ) a * (npf * nqg) ∂μ := by
      refine lintegral_congr fun a => ?_
      rw [Pi.mul_apply, fun_eq_funMulInvSnorm_mul_eLpNorm f hf_nonzero hf_nontop,
        fun_eq_funMulInvSnorm_mul_eLpNorm g hg_nonzero hg_nontop, Pi.mul_apply]
      ring
    _ ≤ npf * nqg := by
      rw [lintegral_mul_const' (npf * nqg) _
          (by simp [npf, nqg, hf_nontop, hg_nontop, hf_nonzero, hg_nonzero, ENNReal.mul_eq_top])]
      refine mul_le_of_le_one_left' ?_
      have hf1 := lintegral_rpow_funMulInvSnorm_eq_one hpq.pos hf_nonzero hf_nontop
      have hg1 := lintegral_rpow_funMulInvSnorm_eq_one hpq.symm.pos hg_nonzero hg_nontop
      exact lintegral_mul_le_one_of_lintegral_rpow_eq_one hpq (hf.mul_const _) hf1 hg1