English
If f ≫ g = 0 in a category with HasZeroMorphisms, and there is epi on factorThruImageSubobject f, then (imageSubobject f).arrow ≫ g = 0.
Русский
Если gh = 0 и существует эпиморфизм factorThruImageSubobject f, то (imageSubobject f).arrow ∘ g = 0.
LaTeX
$$$[HasZeroMorphisms\ C] \Rightarrow [Epi(\mathrm{factorThruImageSubobject} f)] \Rightarrow (\mathrm{imageSubobject} f).\mathrm{arrow} \circ g = 0 \text{ when } f \circ g = 0$$$
Lean4
theorem imageSubobject_arrow_comp_eq_zero [HasZeroMorphisms C] {X Y Z : C} {f : X ⟶ Y} {g : Y ⟶ Z} [HasImage f]
[Epi (factorThruImageSubobject f)] (h : f ≫ g = 0) : (imageSubobject f).arrow ≫ g = 0 :=
zero_of_epi_comp (factorThruImageSubobject f) <| by simp [h]