C : Type u
inst✝¹ : Category C
inst✝ : NonPreadditiveAbelian C
X Y : C
a b c d : X ⟶ Y
⊢ prod.lift (prod.lift a b ≫ σ) (prod.lift c d ≫ σ) ≫ σ = a - b - (c - d)
C : Type u
inst✝¹ : Category C
inst✝ : NonPreadditiveAbelian C
X Y : C
a b c d : X ⟶ Y
⊢ a - c - (b - d) = a - b - (c - d)
rw [sub_def, ← lift_sub_lift, sub_def, Category.assoc, σ_comp, prod.lift_map_assoc]
no goals
C : Type u
inst✝¹ : Category C
inst✝ : NonPreadditiveAbelian C
X Y : C
a b c d : X ⟶ Y
⊢ prod.lift (prod.lift a b ≫ σ) (prod.lift c d ≫ σ) ≫ σ = a - b - (c - d)
rfl