-- Mathlib/SetTheory/Cardinal/Arithmetic.lean
theorem ciSup_add (hf : BddAbove (range f)) (c : Cardinal.{v}) :
    (⨆ i, f i) + c = ⨆ i, f i + c

Proof state:
case inr
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ℵ₀ ≤ ⨆ i, f i
⊢ ⨆ i, f i ≤ ⨆ i, f i + c ∧ c ≤ ⨆ i, f i + c

Tactic:
exact ⟨ciSup_mono bdd fun i ↦ self_le_add_right _ c,
  (self_le_add_left _ _).trans (le_ciSup bdd <| Classical.arbitrary ι)⟩

Result:
no goals

Proof state:
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Tactic:
obtain hs | hs := lt_or_le (⨆ i, f i) ℵ₀

Result:
case inl
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ⨆ i, f i < ℵ₀
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

case inr
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ℵ₀ ≤ ⨆ i, f i
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Proof state:
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
⊢ (⨆ i, f i) + c = ⨆ i, f i + c

Tactic:
have : ∀ i, f i + c ≤ (⨆ i, f i) + c := fun i ↦ add_le_add_right (le_ciSup hf i) c

Result:
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
⊢ (⨆ i, f i) + c = ⨆ i, f i + c

Proof state:
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
⊢ (⨆ i, f i) + c = ⨆ i, f i + c

Tactic:
refine le_antisymm ?_ (ciSup_le' this)

Result:
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Proof state:
case inl.intro
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ⨆ i, f i < ℵ₀
i : ι
hi : f i = ⨆ i, f i
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Tactic:
exact hi ▸ le_ciSup bdd i

Result:
no goals

Proof state:
case inr
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ℵ₀ ≤ ⨆ i, f i
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Tactic:
rw [add_eq_max hs, max_le_iff]

Result:
case inr
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ℵ₀ ≤ ⨆ i, f i
⊢ ⨆ i, f i ≤ ⨆ i, f i + c ∧ c ≤ ⨆ i, f i + c

Proof state:
case inl
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ⨆ i, f i < ℵ₀
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c

Tactic:
obtain ⟨i, hi⟩ := exists_eq_of_iSup_eq_of_not_isSuccLimit
  f hf (not_isSuccLimit_of_lt_aleph0 hs) rfl

Result:
case inl.intro
ι : Type u
f : ι → Cardinal.{v}
inst✝ : Nonempty ι
hf : BddAbove (range f)
c : Cardinal.{v}
this : ∀ (i : ι), f i + c ≤ (⨆ i, f i) + c
bdd : BddAbove (range fun x => f x + c)
hs : ⨆ i, f i < ℵ₀
i : ι
hi : f i = ⨆ i, f i
⊢ (⨆ i, f i) + c ≤ ⨆ i, f i + c