Module: Mathlib.CategoryTheory.Adhesive.Basic

Goal state before:
pp: case h'_w.h'_w
J : Type v'
inst✝⁴ : Category.{u', v'} J
C : Type u
inst✝³ : Category.{v, u} C
W X Y Z✝ : C
f✝ : W ⟶ X
g✝ : W ⟶ Y
h : X ⟶ Z✝
i : Y ⟶ Z✝
inst✝² : Adhesive C
Z A B : C
a : A ⟶ Z
b : B ⟶ Z
inst✝¹ : Mono a
inst✝ : Mono b
K : C
f g : K ⟶ pushout (fst a b) (snd a b)
w : f ≫ pushout.desc a b ⋯ = g ≫ pushout.desc a b ⋯
u : A ⟶ pushout (fst a b) (snd a b) := inl (fst a b) (snd a b)
v : B ⟶ pushout (fst a b) (snd a b) := inr (fst a b) (snd a b)
this✝² : Mono u := mono_of_isPushout_of_mono_right (of_hasPushout (fst a b) (snd a b))
this✝¹ : Mono v := mono_of_isPushout_of_mono_left (of_hasPushout (fst a b) (snd a b))
sq_f_u : IsPullback (fst f u) (snd f u) f u := of_hasPullback f u
sq_f_v : IsPullback (fst f v) (snd f v) f v := of_hasPullback f v
sq_g_u : IsPullback (fst g u) (snd g u) g u := of_hasPullback g u
sq_g_v : IsPullback (fst g v) (snd g v) g v := of_hasPullback g v
l₁ : pullback f u ⟶ K := fst f u
f₁ : pullback f u ⟶ A := snd f u
l₂ : pullback f v ⟶ K := fst f v
f₂ : pullback f v ⟶ B := snd f v
m₁ : pullback g u ⟶ K := fst g u
g₁ : pullback g u ⟶ A := snd g u
m₂ : pullback g v ⟶ K := fst g v
g₂ : pullback g v ⟶ B := snd g v
w✝² : C
f' : w✝² ⟶ pullback f u
w✝¹ : w✝² ⟶ pullback f v
w✝ : w✝² ⟶ pullback a b
p₁ : IsPullback f' w✝ (snd f u) (fst a b)
left✝ : IsPullback w✝¹ w✝ (snd f v) (snd a b)
h₁ : IsPushout f' w✝¹ (fst f u) (fst f v)
this✝ : Mono f' := Eq.mpr (id (congrArg (fun _a ↦ Mono _a) (Eq.symm (isoPullback_hom_fst p₁)))) inferInstance
sq₁₁ : IsPullback (fst m₁ l₁) (snd m₁ l₁) m₁ l₁ := of_hasPullback m₁ l₁
sq₁₂ : IsPullback (fst m₁ l₂) (snd m₁ l₂) m₁ l₂ := of_hasPullback m₁ l₂
this : Mono (u ≫ pushout.desc a b ⋯) :=
  Eq.mpr (id (congrArg (fun _a ↦ Mono _a) (pushout.inl_desc a b pullback.condition))) inst✝¹
⊢ snd m₁ l₁ ≫ snd f u = fst m₁ l₁ ≫ snd g u

Tactic:
← cancel_mono (u ≫ pushout.desc a b pullback.condition),

Goal state after:
case h'_w.h'_w
J : Type v'
inst✝⁴ : Category.{u', v'} J
C : Type u
inst✝³ : Category.{v, u} C
W X Y Z✝ : C
f✝ : W ⟶ X
g✝ : W ⟶ Y
h : X ⟶ Z✝
i : Y ⟶ Z✝
inst✝² : Adhesive C
Z A B : C
a : A ⟶ Z
b : B ⟶ Z
inst✝¹ : Mono a
inst✝ : Mono b
K : C
f g : K ⟶ pushout (fst a b) (snd a b)
w : f ≫ pushout.desc a b ⋯ = g ≫ pushout.desc a b ⋯
u : A ⟶ pushout (fst a b) (snd a b) := inl (fst a b) (snd a b)
v : B ⟶ pushout (fst a b) (snd a b) := inr (fst a b) (snd a b)
this✝² : Mono u := mono_of_isPushout_of_mono_right (of_hasPushout (fst a b) (snd a b))
this✝¹ : Mono v := mono_of_isPushout_of_mono_left (of_hasPushout (fst a b) (snd a b))
sq_f_u : IsPullback (fst f u) (snd f u) f u := of_hasPullback f u
sq_f_v : IsPullback (fst f v) (snd f v) f v := of_hasPullback f v
sq_g_u : IsPullback (fst g u) (snd g u) g u := of_hasPullback g u
sq_g_v : IsPullback (fst g v) (snd g v) g v := of_hasPullback g v
l₁ : pullback f u ⟶ K := fst f u
f₁ : pullback f u ⟶ A := snd f u
l₂ : pullback f v ⟶ K := fst f v
f₂ : pullback f v ⟶ B := snd f v
m₁ : pullback g u ⟶ K := fst g u
g₁ : pullback g u ⟶ A := snd g u
m₂ : pullback g v ⟶ K := fst g v
g₂ : pullback g v ⟶ B := snd g v
w✝² : C
f' : w✝² ⟶ pullback f u
w✝¹ : w✝² ⟶ pullback f v
w✝ : w✝² ⟶ pullback a b
p₁ : IsPullback f' w✝ (snd f u) (fst a b)
left✝ : IsPullback w✝¹ w✝ (snd f v) (snd a b)
h₁ : IsPushout f' w✝¹ (fst f u) (fst f v)
this✝ : Mono f' := Eq.mpr (id (congrArg (fun _a ↦ Mono _a) (Eq.symm (isoPullback_hom_fst p₁)))) inferInstance
sq₁₁ : IsPullback (fst m₁ l₁) (snd m₁ l₁) m₁ l₁ := of_hasPullback m₁ l₁
sq₁₂ : IsPullback (fst m₁ l₂) (snd m₁ l₂) m₁ l₂ := of_hasPullback m₁ l₂
this : Mono (u ≫ pushout.desc a b ⋯) :=
  Eq.mpr (id (congrArg (fun _a ↦ Mono _a) (pushout.inl_desc a b pullback.condition))) inst✝¹
⊢ (snd m₁ l₁ ≫ snd f u) ≫ u ≫ pushout.desc a b ⋯ = (fst m₁ l₁ ≫ snd g u) ≫ u ≫ pushout.desc a b ⋯