theorem Memℒp.snorm_indicator_norm_ge_le (hf : Memℒp f p μ) (hmeas : StronglyMeasurable f) {ε : ℝ}
    (hε : 0 < ε) : ∃ M : ℝ, snorm ({ x | M ≤ ‖f x‖₊ }.indicator f) p μ ≤ ENNReal.ofReal ε := by
  by_cases hp_ne_zero : p = 0
  · refine' ⟨1, hp_ne_zero.symm ▸ _⟩
    simp [snorm_exponent_zero]
  by_cases hp_ne_top : p = ∞
  · subst hp_ne_top
    obtain ⟨M, hM⟩ := hf.snormEssSup_indicator_norm_ge_eq_zero μ hmeas
    refine' ⟨M, _⟩
    simp only [snorm_exponent_top, hM, zero_le]
  obtain ⟨M, hM', hM⟩ := Memℒp.integral_indicator_norm_ge_nonneg_le
    (μ := μ) (hf.norm_rpow hp_ne_zero hp_ne_top) (Real.rpow_pos_of_pos hε p.toReal)
  refine' ⟨M ^ (1 / p.toReal), _⟩
  rw [snorm_eq_lintegral_rpow_nnnorm hp_ne_zero hp_ne_top, ← ENNReal.rpow_one (ENNReal.ofReal ε)]
  conv_rhs => rw [← mul_one_div_cancel (ENNReal.toReal_pos hp_ne_zero hp_ne_top).ne.symm]
  rw [ENNReal.rpow_mul,
    ENNReal.rpow_le_rpow_iff (one_div_pos.2 <| ENNReal.toReal_pos hp_ne_zero hp_ne_top),
    ENNReal.ofReal_rpow_of_pos hε]
  convert hM
  rename_i x
  rw [ENNReal.coe_rpow_of_nonneg _ ENNReal.toReal_nonneg, nnnorm_indicator_eq_indicator_nnnorm,
    nnnorm_indicator_eq_indicator_nnnorm]
  have hiff : M ^ (1 / p.toReal) ≤ ‖f x‖₊ ↔ M ≤ ‖‖f x‖ ^ p.toReal‖₊ := by
    rw [coe_nnnorm, coe_nnnorm, Real.norm_rpow_of_nonneg (norm_nonneg _), norm_norm,
      ← Real.rpow_le_rpow_iff hM' (Real.rpow_nonneg_of_nonneg (norm_nonneg _) _)
        (one_div_pos.2 <| ENNReal.toReal_pos hp_ne_zero hp_ne_top), ← Real.rpow_mul (norm_nonneg _),
      mul_one_div_cancel (ENNReal.toReal_pos hp_ne_zero hp_ne_top).ne.symm, Real.rpow_one]
  by_cases hx : x ∈ { x : α | M ^ (1 / p.toReal) ≤ ‖f x‖₊ }
  · rw [Set.indicator_of_mem hx, Set.indicator_of_mem, Real.nnnorm_of_nonneg]; 

Proof state:
case pos
α : Type u_1
β : Type u_2
ι : Type u_3
m : MeasurableSpace α
μ : Measure α
inst✝ : NormedAddCommGroup β
p : ℝ≥0∞
f : α → β
hf : Memℒp f p
hmeas : StronglyMeasurable f
ε : ℝ
hε : 0 < ε
hp_ne_zero : ¬p = 0
hp_ne_top : ¬p = ⊤
M : ℝ
hM' : 0 ≤ M
hM :
  ∫⁻ (x : α), ↑‖Set.indicator {x | M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊} (fun x => ‖f x‖ ^ ENNReal.toReal p) x‖₊ ∂μ ≤
    ENNReal.ofReal (ε ^ ENNReal.toReal p)
x : α
hiff : M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊ ↔ M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊
hx : x ∈ {x | M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊}
⊢ ↑(‖f x‖₊ ^ ENNReal.toReal p) = ↑{ val := ‖f x‖ ^ ENNReal.toReal p, property := ?pos✝ }
case pos
α : Type u_1
β : Type u_2
ι : Type u_3
m : MeasurableSpace α
μ : Measure α
inst✝ : NormedAddCommGroup β
p : ℝ≥0∞
f : α → β
hf : Memℒp f p
hmeas : StronglyMeasurable f
ε : ℝ
hε : 0 < ε
hp_ne_zero : ¬p = 0
hp_ne_top : ¬p = ⊤
M : ℝ
hM' : 0 ≤ M
hM :
  ∫⁻ (x : α), ↑‖Set.indicator {x | M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊} (fun x => ‖f x‖ ^ ENNReal.toReal p) x‖₊ ∂μ ≤
    ENNReal.ofReal (ε ^ ENNReal.toReal p)
x : α
hiff : M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊ ↔ M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊
hx : x ∈ {x | M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊}
⊢ 0 ≤ ‖f x‖ ^ ENNReal.toReal p
case pos.h
α : Type u_1
β : Type u_2
ι : Type u_3
m : MeasurableSpace α
μ : Measure α
inst✝ : NormedAddCommGroup β
p : ℝ≥0∞
f : α → β
hf : Memℒp f p
hmeas : StronglyMeasurable f
ε : ℝ
hε : 0 < ε
hp_ne_zero : ¬p = 0
hp_ne_top : ¬p = ⊤
M : ℝ
hM' : 0 ≤ M
hM :
  ∫⁻ (x : α), ↑‖Set.indicator {x | M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊} (fun x => ‖f x‖ ^ ENNReal.toReal p) x‖₊ ∂μ ≤
    ENNReal.ofReal (ε ^ ENNReal.toReal p)
x : α
hiff : M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊ ↔ M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊
hx : x ∈ {x | M ^ (1 / ENNReal.toReal p) ≤ ↑‖f x‖₊}
⊢ x ∈ {x | M ≤ ↑‖‖f x‖ ^ ENNReal.toReal p‖₊}

Next tactic:
rfl