∀ {X : SSet.Truncated 2} [X.Quasicategory₂]
  {x y : X.obj (Opposite.op { obj := SimplexCategory.mk 0, property := SSet.Truncated.Quasicategory₂._proof_1 })}
  {f g : SSet.Truncated.Edge x y}, SSet.Truncated.HomotopicR f g → SSet.Truncated.HomotopicL f g