∀ {X : SSet.Truncated 2} {x y : X.obj (Opposite.op { obj := { len := 0 }, property := SSet.Truncated.Edge._proof_1 })}
  (e : SSet.Truncated.Edge x y),
  X.map (SimplexCategory.Truncated.δ₂ 2 SSet.Truncated.Edge._proof_2 SSet.Truncated.Edge.CompStruct._proof_2).op
      (X.map (SimplexCategory.Truncated.σ₂ 0 SSet.Truncated.Edge.CompStruct._proof_2 SSet.Truncated.Edge._proof_2).op
        e.edge) =
    (SSet.Truncated.Edge.id x).edge