-- Mathlib/CategoryTheory/Limits/Shapes/WidePullbacks.lean
theorem eq_lift_of_comp_eq (g : X ⟶ widePullback _ _ arrows) :
    (∀ j : J, g ≫ π arrows j = fs j) → g ≫ base arrows = f → g = lift f fs w

Proof state:
case x.some
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
val✝ : J
⊢ g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app (some val✝) =
    (WidePullbackShape.mkCone f fs w).π.app (some val✝)

Tactic:
apply h1

Result:
no goals

Proof state:
case x
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ ∀ (j : WidePullbackShape J),
    g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app j = (WidePullbackShape.mkCone f fs w).π.app j

Tactic:
rintro (_ | _)

Result:
case x.none
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app none =
    (WidePullbackShape.mkCone f fs w).π.app none

case x.some
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
val✝ : J
⊢ g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app (some val✝) =
    (WidePullbackShape.mkCone f fs w).π.app (some val✝)

Proof state:
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ g = lift f fs w

Tactic:
apply
  (limit.isLimit (WidePullbackShape.wideCospan B objs arrows)).uniq
    (WidePullbackShape.mkCone f fs <| w)

Result:
case x
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ ∀ (j : WidePullbackShape J),
    g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app j = (WidePullbackShape.mkCone f fs w).π.app j

Proof state:
case x.none
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ g ≫ (limit.cone (WidePullbackShape.wideCospan B objs arrows)).π.app none =
    (WidePullbackShape.mkCone f fs w).π.app none

Tactic:
apply h2

Result:
no goals

Proof state:
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
⊢ (∀ (j : J), g ≫ π arrows j = fs j) → g ≫ base arrows = f → g = lift f fs w

Tactic:
intro h1 h2

Result:
J : Type w
C : Type u
inst✝¹ : Category.{v, u} C
B : C
objs : J → C
arrows : (j : J) → objs j ⟶ B
inst✝ : HasWidePullback B objs arrows
X : C
f : X ⟶ B
fs : (j : J) → X ⟶ objs j
w : ∀ (j : J), fs j ≫ arrows j = f
g : X ⟶ widePullback B objs arrows
h1 : ∀ (j : J), g ≫ π arrows j = fs j
h2 : g ≫ base arrows = f
⊢ g = lift f fs w