Introduce the corresponding concepts of cover and hull through Q gets the properties of τ-injective,τ-projective,τ-pisible and τ-copisible,discuss the properties of τ-torsion injective hull, τ-torsion projective cover,τ-torsionfree pisible hull and τ-torsionfree copisible cover, τ-injective hull E_τ(M) is characterized by using them.
讨论τ-挠内射包,τ-挠投射盖,τ-挠自由可除包和τ-挠自由余可除盖的性质,并利用它们刻画了τ-内射包Eτ(M)。