∀ {ι : Type u_1} [inst : DecidableEq ι] (i j k : ι)
  (x : CategoryTheory.Pairwise.pair i j ⟶ CategoryTheory.Pairwise.single k),
  x ∈
    (if h : i = k then
        {CategoryTheory.CategoryStruct.comp (CategoryTheory.Pairwise.Hom.left i j) (CategoryTheory.eqToHom ⋯)}
      else ∅) ∪
      if h : j = k then
        {CategoryTheory.CategoryStruct.comp (CategoryTheory.Pairwise.Hom.right i j) (CategoryTheory.eqToHom ⋯)}
      else ∅