-- Mathlib/Probability/Kernel/WithDensity.lean
theorem isSFiniteKernel_withDensity_of_isFiniteKernel (κ : Kernel α β) [IsFiniteKernel κ]
    (hf_ne_top : ∀ a b, f a b ≠ ∞) : IsSFiniteKernel (withDensity κ f)

Proof state:
case pos
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
hf_eq_tsum : f = ∑' (n : ℕ), fs n
⊢ IsSFiniteKernel (Kernel.sum fun n => κ.withDensity (fs n))

Tactic:
refine isSFiniteKernel_sum (hκs := fun n => ?_)

Result:
case pos
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
hf_eq_tsum : f = ∑' (n : ℕ), fs n
n : ℕ
⊢ IsSFiniteKernel (κ.withDensity (fs n))

Proof state:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
a : α
b : β
⊢ Summable fun i => fs i a b

Tactic:
suffices ∀ n, n ∉ Finset.range ⌈(f a b).toReal⌉₊ → fs n a b = 0 from
  summable_of_ne_finset_zero this

Result:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
a : α
b : β
⊢ ∀ n ∉ Finset.range ⌈(f a b).toReal⌉₊, fs n a b = 0

Proof state:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
a : α
b : β
n : ℕ
hn_not_mem : n ∉ Finset.range ⌈(f a b).toReal⌉₊
⊢ fs n a b = 0

Tactic:
rw [Finset.mem_range, not_lt] at hn_not_mem

Result:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
a : α
b : β
n : ℕ
hn_not_mem : ⌈(f a b).toReal⌉₊ ≤ n
⊢ fs n a b = 0

Proof state:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
⊢ ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n

Tactic:
intro a b n hn

Result:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
a : α
b : β
n : ℕ
hn : ⌈(f a b).toReal⌉₊ ≤ n
⊢ f a b ≤ ↑n

Proof state:
case pos
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
hf_eq_tsum : f = ∑' (n : ℕ), fs n
n : ℕ
a : α
b : β
⊢ fs n a b ≤ ↑(n + 1)

Tactic:
calc
  fs n a b ≤ min (f a b) (n + 1) := tsub_le_self
  _ ≤ n + 1 := min_le_right _ _
  _ = ↑(n + 1) := by norm_cast

Result:
no goals

Proof state:
case pos
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
⊢ IsSFiniteKernel (κ.withDensity f)

Tactic:
have h_zero : ∀ a b n, ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0 := by
  intro a b n hn
  suffices min (f a b) (n + 1) = f a b ∧ min (f a b) n = f a b by
    simp_rw [fs, this.1, this.2, tsub_self (f a b)]
  exact ⟨min_eq_left ((h_le a b n hn).trans (le_add_of_nonneg_right zero_le_one)),
    min_eq_left (h_le a b n hn)⟩

Result:
case pos
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
⊢ IsSFiniteKernel (κ.withDensity f)

Proof state:
case h.h
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
h_sum_a : ∀ (a : α), Summable fun n => fs n a
a : α
b : β
h_finset_sum : ∀ (n : ℕ), ∑ i ∈ Finset.range n, fs i a b = f a b ⊓ ↑n
⊢ ∃ a_1, ∀ b_1 ≥ a_1, f a b = f a b ⊓ ↑b_1

Tactic:
exact ⟨⌈(f a b).toReal⌉₊, fun n hn => (min_eq_left (h_le a b n hn)).symm⟩

Result:
no goals

Proof state:
α : Type u_1
β : Type u_2
mα : MeasurableSpace α
mβ : MeasurableSpace β
f : α → β → ℝ≥0∞
κ : Kernel α β
inst✝ : IsFiniteKernel κ
hf_ne_top : ∀ (a : α) (b : β), f a b ≠ ⊤
hf : Measurable (Function.uncurry f)
fs : ℕ → α → β → ℝ≥0∞ := fun n a b => f a b ⊓ (↑n + 1) - f a b ⊓ ↑n
h_le : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → f a b ≤ ↑n
h_zero : ∀ (a : α) (b : β) (n : ℕ), ⌈(f a b).toReal⌉₊ ≤ n → fs n a b = 0
a : α
b : β
n : ℕ
hn_not_mem : ⌈(f a b).toReal⌉₊ ≤ n
⊢ fs n a b = 0

Tactic:
exact h_zero a b n hn_not_mem

Result:
no goals