-- Mathlib/CategoryTheory/Limits/Shapes/Pullback/Assoc.lean
theorem inl_inl_pushoutAssoc_hom [HasPushout (g₃ ≫ (pushout.inr _ _ : X₂ ⟶ Y₁)) g₄]
    [HasPushout g₁ (g₂ ≫ (pushout.inl _ _ : X₂ ⟶ Y₂))] :
    pushout.inl _ _ ≫ pushout.inl _ _ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom = pushout.inl _ _

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl g₁ g₂ ≫
      pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄))
        (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄)) ⋯ =
    pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄)

Tactic:
exact pushout.inl_desc _ _ _

Result:
no goals

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl g₁ g₂ ≫ pushout.inl (g₃ ≫ pushout.inr g₁ g₂) g₄ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom =
    pushout.inl g₁ g₂ ≫
      pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄))
        (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄)) ⋯

Tactic:
congr 1

Result:
case e_a
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl (g₃ ≫ pushout.inr g₁ g₂) g₄ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom =
    pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄)) (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄))
      ⋯

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl g₁ g₂ ≫ pushout.inl (g₃ ≫ pushout.inr g₁ g₂) g₄ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom =
    pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄)

Tactic:
trans f₁ ≫ l₁

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl g₁ g₂ ≫ pushout.inl (g₃ ≫ pushout.inr g₁ g₂) g₄ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom =
    pushout.inl g₁ g₂ ≫
      pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄))
        (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄)) ⋯

C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl g₁ g₂ ≫
      pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄))
        (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄)) ⋯ =
    pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄)

Proof state:
case e_a
C : Type u
inst✝⁴ : Category.{v, u} C
X₁ X₂ X₃ Z₁ Z₂ : C
g₁ : Z₁ ⟶ X₁
g₂ : Z₁ ⟶ X₂
g₃ : Z₂ ⟶ X₂
g₄ : Z₂ ⟶ X₃
inst✝³ : HasPushout g₁ g₂
inst✝² : HasPushout g₃ g₄
inst✝¹ : HasPushout (g₃ ≫ pushout.inr g₁ g₂) g₄
inst✝ : HasPushout g₁ (g₂ ≫ pushout.inl g₃ g₄)
⊢ pushout.inl (g₃ ≫ pushout.inr g₁ g₂) g₄ ≫ (pushoutAssoc g₁ g₂ g₃ g₄).hom =
    pushout.desc (pushout.inl g₁ (g₂ ≫ pushout.inl g₃ g₄)) (pushout.inl g₃ g₄ ≫ pushout.inr g₁ (g₂ ≫ pushout.inl g₃ g₄))
      ⋯

Tactic:
exact
  (pushoutPushoutLeftIsPushout g₁ g₂ g₃ g₄).comp_coconePointUniqueUpToIso_hom _
    WalkingCospan.left

Result:
no goals