∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Limits.HasZeroMorphisms C]
  [inst_2 : CategoryTheory.Limits.HasKernels C] (X : C) (x : Cᵒᵖ) (f : x ⟶ Opposite.op X),
  CategoryTheory.Mono (CategoryTheory.Limits.equalizer.ι f.unop 0)