theorem extracted_formal_statement_143.{u_1} {E : Type u_1} [inst : NormedAddCommGroup E] [inst_1 : InnerProductSpace ℝ E]
  [inst_2 : CompleteSpace E] {f : E → ℝ} (xm x₀ : E) {alg : subgradient_method f x₀} {s : ℝ}
  (hm : IsMinOn f Set.univ xm) (ha' : ∀ (n : ℕ), subgradient_method.a f x₀ n * ‖subgradient_method.g f x₀ n‖ = s)
  (hs : s > 0) (k : ℕ) (hnek : Nonempty { x // x ∈ Finset.range (k + 1) })
  (h' : ∀ ⦃x g : E⦄, g ∈ SubderivAt f x → ‖g‖ ≤ ↑(subgradient_method.G f x₀))
  (h₁ :
    ∀ ⦃i : ℕ⦄,
      i ≥ 0 ∧ i ≤ k →
        ‖subgradient_method.x f x₀ (i + 1) - xm‖ ^ 2 ≤
          ‖subgradient_method.x f x₀ i - xm‖ ^ 2 -
              2 * subgradient_method.a f x₀ i *
                (sInf {x | ∃ i ∈ Finset.range (k + 1), f (subgradient_method.x f x₀ i) = x} - f xm) +
            ‖subgradient_method.a f x₀ i‖ ^ 2 * ‖subgradient_method.g f x₀ i‖ ^ 2)
  (h₁' :
    ∀ ⦃i : ℕ⦄,
      i ≥ 0 ∧ i ≤ k →
        subgradient_method.a f x₀ i *
            (2 * (sInf {x | ∃ i ∈ Finset.range (k + 1), f (subgradient_method.x f x₀ i) = x} - f xm)) ≤
          ‖subgradient_method.x f x₀ i - xm‖ ^ 2 - ‖subgradient_method.x f x₀ (i + 1) - xm‖ ^ 2 + s ^ 2)
  (h₂ :
    (2 * ∑ i ∈ Finset.range (k + 1), subgradient_method.a f x₀ i) *
        (sInf {x | ∃ i < k + 1, f (subgradient_method.x f x₀ i) = x} - f xm) ≤
      ‖x₀ - xm‖ ^ 2 - ‖subgradient_method.x f x₀ (k + 1) - xm‖ ^ 2 + (↑k + 1) * s ^ 2)
  (hG : ↑(subgradient_method.G f x₀) > 0)
  (inq₁ : ∑ x ∈ Finset.range (k + 1), subgradient_method.a f x₀ x ≥ (↑k + 1) * (s / ↑(subgradient_method.G f x₀)))
  (hpos₁ : (↑k + 1) * (s / ↑(subgradient_method.G f x₀)) > 0)
  (hpos₁' : 2 * (↑k + 1) * (s / ↑(subgradient_method.G f x₀)) > 0)
  (heq :
    (Set.range fun x => f (subgradient_method.x f x₀ ↑x)) = {x | ∃ i < k + 1, f (subgradient_method.x f x₀ i) = x}) :
  (Set.range fun x => f (subgradient_method.x f x₀ ↑x)).Nonempty := sorry

State before:
case a0.a.h₁
E : Type u_1
inst✝² : NormedAddCommGroup E
inst✝¹ : InnerProductSpace ℝ E
inst✝ : CompleteSpace E
f : E → ℝ
xm x₀ : E
alg : subgradient_method f x₀
s : ℝ
hm : IsMinOn f Set.univ xm
ha' : ∀ (n : ℕ), subgradient_method.a f x₀ n * ‖subgradient_method.g f x₀ n‖ = s
hs : s > 0
k : ℕ
hnek : Nonempty { x // x ∈ Finset.range (k + 1) }
h' : ∀ ⦃x g : E⦄, g ∈ SubderivAt f x → ‖g‖ ≤ ↑(subgradient_method.G f x₀)
h₁ :
  ∀ ⦃i : ℕ⦄,
    i ≥ 0 ∧ i ≤ k →
      ‖subgradient_method.x f x₀ (i + 1) - xm‖ ^ 2 ≤
        ‖subgradient_method.x f x₀ i - xm‖ ^ 2 -
            2 * subgradient_method.a f x₀ i *
              (sInf {x | ∃ i ∈ Finset.range (k + 1), f (subgradient_method.x f x₀ i) = x} - f xm) +
          ‖subgradient_method.a f x₀ i‖ ^ 2 * ‖subgradient_method.g f x₀ i‖ ^ 2
h₁' :
  ∀ ⦃i : ℕ⦄,
    i ≥ 0 ∧ i ≤ k →
      subgradient_method.a f x₀ i *
          (2 * (sInf {x | ∃ i ∈ Finset.range (k + 1), f (subgradient_method.x f x₀ i) = x} - f xm)) ≤
        ‖subgradient_method.x f x₀ i - xm‖ ^ 2 - ‖subgradient_method.x f x₀ (i + 1) - xm‖ ^ 2 + s ^ 2
h₂ :
  (2 * ∑ i ∈ Finset.range (k + 1), subgradient_method.a f x₀ i) *
      (sInf {x | ∃ i < k + 1, f (subgradient_method.x f x₀ i) = x} - f xm) ≤
    ‖x₀ - xm‖ ^ 2 - ‖subgradient_method.x f x₀ (k + 1) - xm‖ ^ 2 + (↑k + 1) * s ^ 2
hG : ↑(subgradient_method.G f x₀) > 0
inq₁ : ∑ x ∈ Finset.range (k + 1), subgradient_method.a f x₀ x ≥ (↑k + 1) * (s / ↑(subgradient_method.G f x₀))
hpos₁ : (↑k + 1) * (s / ↑(subgradient_method.G f x₀)) > 0
hpos₁' : 2 * (↑k + 1) * (s / ↑(subgradient_method.G f x₀)) > 0
heq : (Set.range fun x => f (subgradient_method.x f x₀ ↑x)) = {x | ∃ i < k + 1, f (subgradient_method.x f x₀ i) = x}
⊢ (Set.range fun x => f (subgradient_method.x f x₀ ↑x)).Nonempty

Tactic: apply Set.range_nonempty

State after:

Relevant lemmas:
Set.range_nonempty : ∀ {α : Type u_1} {ι : Sort u_4} [h : Nonempty ι] (f : ι → α), (Set.range f).Nonempty