-- Mathlib/Data/Sum/Interval.lean
theorem mem_sumLift₂ :
    c ∈ sumLift₂ f g a b ↔
      (∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
        ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Proof state:
case mp.inr.inr.intro.intro
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₂
b : β₂
c : γ₂
hc : c ∈ g a b
⊢ (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ Embedding.inr c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
    ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ Embedding.inr c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
exact Or.inr ⟨a, b, c, rfl, rfl, rfl, hc⟩

Result:
no goals

Proof state:
case mp.inr.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₁
⊢ c ∈ sumLift₂ f g (inr a) (inl b) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
refine fun h ↦ (not_mem_empty _ h).elim

Result:
no goals

Proof state:
case mpr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁ ⊕ α₂
b : β₁ ⊕ β₂
c : γ₁ ⊕ γ₂
⊢ ((∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂) →
    c ∈ sumLift₂ f g a b

Tactic:
rintro (⟨a, b, c, rfl, rfl, rfl, h⟩ | ⟨a, b, c, rfl, rfl, rfl, h⟩) <;> exact mem_map_of_mem _ h

Result:
no goals

Proof state:
case mp.inl.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₁
b : β₁
⊢ (∃ a_1 ∈ f a b, Embedding.inl a_1 = c) →
    (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
rintro ⟨c, hc, rfl⟩

Result:
case mp.inl.inl.intro.intro
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁
b : β₁
c : γ₁
hc : c ∈ f a b
⊢ (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inl b = inl b₁ ∧ Embedding.inl c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
    ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inl b = inr b₂ ∧ Embedding.inl c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Proof state:
case mp.inr.inr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₂
⊢ (∃ a_1 ∈ g a b, Embedding.inr a_1 = c) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
rintro ⟨c, hc, rfl⟩

Result:
case mp.inr.inr.intro.intro
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₂
b : β₂
c : γ₂
hc : c ∈ g a b
⊢ (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ Embedding.inr c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
    ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ Embedding.inr c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Proof state:
case mp.inl.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₁
b : β₁
⊢ c ∈ sumLift₂ f g (inl a) (inl b) →
    (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
rw [sumLift₂, mem_map]

Result:
case mp.inl.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₁
b : β₁
⊢ (∃ a_1 ∈ f a b, Embedding.inl a_1 = c) →
    (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Proof state:
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁ ⊕ α₂
b : β₁ ⊕ β₂
c : γ₁ ⊕ γ₂
⊢ c ∈ sumLift₂ f g a b ↔
    (∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
constructor

Result:
case mp
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁ ⊕ α₂
b : β₁ ⊕ β₂
c : γ₁ ⊕ γ₂
⊢ c ∈ sumLift₂ f g a b →
    (∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

case mpr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁ ⊕ α₂
b : β₁ ⊕ β₂
c : γ₁ ⊕ γ₂
⊢ ((∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂) →
    c ∈ sumLift₂ f g a b

Proof state:
case mp.inr.inr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₂
⊢ c ∈ sumLift₂ f g (inr a) (inr b) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
rw [sumLift₂, mem_map]

Result:
case mp.inr.inr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₂
⊢ (∃ a_1 ∈ g a b, Embedding.inr a_1 = c) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Proof state:
case mp
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
a : α₁ ⊕ α₂
b : β₁ ⊕ β₂
c : γ₁ ⊕ γ₂
⊢ c ∈ sumLift₂ f g a b →
    (∃ a₁ b₁ c₁, a = inl a₁ ∧ b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, a = inr a₂ ∧ b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

Tactic:
rcases a with a | a <;> rcases b with b | b

Result:
case mp.inl.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₁
b : β₁
⊢ c ∈ sumLift₂ f g (inl a) (inl b) →
    (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

case mp.inl.inr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₁
b : β₂
⊢ c ∈ sumLift₂ f g (inl a) (inr b) →
    (∃ a₁ b₁ c₁, inl a = inl a₁ ∧ inr b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inl a = inr a₂ ∧ inr b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

case mp.inr.inl
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₁
⊢ c ∈ sumLift₂ f g (inr a) (inl b) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inl b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inl b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂

case mp.inr.inr
α₁ : Type u_1
α₂ : Type u_2
β₁ : Type u_3
β₂ : Type u_4
γ₁ : Type u_5
γ₂ : Type u_6
f : α₁ → β₁ → Finset γ₁
g : α₂ → β₂ → Finset γ₂
c : γ₁ ⊕ γ₂
a : α₂
b : β₂
⊢ c ∈ sumLift₂ f g (inr a) (inr b) →
    (∃ a₁ b₁ c₁, inr a = inl a₁ ∧ inr b = inl b₁ ∧ c = inl c₁ ∧ c₁ ∈ f a₁ b₁) ∨
      ∃ a₂ b₂ c₂, inr a = inr a₂ ∧ inr b = inr b₂ ∧ c = inr c₂ ∧ c₂ ∈ g a₂ b₂