REFERENCES
- Anderson , F. W. , Fuller , K. R. ( 1974 ). Rings and Categories of Modules . New York : Springer-Verlag .
- Asensio Mayor , J. , Martinez Hernandez , J. ( 1993 ). On flat and projective envelopes . J. Algebra 160 : 434 – 440 .
- Bass , H. ( 1960 ). Finitistic dimension and a homological generalization of semiprimary rings . Trans. Amer. Math. Soc. 95 : 466 – 488 .
- Chase , S. U. ( 1960 ). Direct products of modules . Trans. Amer. Math. Soc. 97 : 457 – 473 .
- Cheatham , T. J. , Stone , D. R. ( 1981 ). Flat and projective character modules . Proc. Amer. Math. Soc. 81 : 175 – 177 .
- Chen , J. L. ( 1996 ). P-projective modules . Comm. Algebra 24 : 821 – 831 .
- Ding , N. Q. , Chen , J. L. (1993). The flat dimensions of injective modules. Manuscripta Math. 78:165–177.
- Ding , N. Q. , Chen , J. L. ( 1993 ). Relative coherence and preenvelopes . Manuscripta Math. 81 : 243 – 262 .
- Ding , N. Q. , Chen , J. L. ( 1996 ). Coherent rings with finite self-FP-injective dimension . Comm. Algebra 24 : 2963 – 2980 .
- Enochs , E. E. ( 1981 ). Injective and flat covers, envelopes and resolvents . Israel J. Math. 39 : 189 – 209 .
- Enochs , E. E. , Jenda , O. M. G. ( 1993 ). Copure injective resolutions, flat resolutions and dimensions . Comment. Math. Univ. Carolinae 34 : 203 – 211 .
- Enochs , E. E. , Jenda , O. M. G. ( 2000 ). Relative Homological Algebra . Berlin-New York : Walter de Gruyter .
- Enochs , E. E. , Jenda , O. M. G. , Lopez-Ramos , J. A. ( 2004 ). The existence of Gorenstein flat covers . Math. Scand. 94 : 46 – 62 .
- Fieldhouse , D. J. ( 1972 ). Character modules, dimension and purity . Glasgow Math. J. 13 : 144 – 146 .
- Göbel , R. , Trlifaj , J. ( 2006 ). Approximations and Endomorphism Algebras of Modules . GEM 41 , Berlin-New York : Walter de Gruyter .
- Jategornkar , A. V. ( 1969 ). A counter example in ring theory and homological algebra . J. Algebra 12 : 418 – 440 .
- Jenda , O. M. G. ( 1988 ). The dual of the grade of a module . Arch. Math. 51 : 297 – 302 .
- Jensen , C. U. ( 1970 ). On the vanishing of . J. Algebra 15 : 151 – 166 .
- Kasch , F. ( 1982 ). Modules and Rings . London-New York : Academic Press .
- Lam , T. Y. ( 1999 ). Lectures on Modules and Rings . New York-Heidelberg-Berlin : Springer-Verlag .
- Mao , L. X. , Ding , N. Q. ( 2005 ). Relative FP-projective modules . Comm. Algebra 33 : 1587 – 1602 .
- Mao , L. X. , Ding , N. Q. ( 2007 ). Global dimension and left derived functors of Hom . Sci. China Ser. A 50 : 887 – 898 .
- Rees , D. ( 1957 ). The grade of an ideal or module . Proc. Cambridge Phil. Soc. 53 : 28 – 42 .
- Rotman , J. J. ( 1979 ). An Introduction to Homological Algebra . New York : Academic Press .
- Smith , P. F. ( 1981 ). Injective modules and prime ideals . Comm. Algebra 9 : 989 – 999 .
- Stenström , B. ( 1970 ). Coherent rings and FP-injective modules . J. London Math. Soc. 2 : 323 – 329 .
- Xu , J. ( 1996 ). Flat Covers of Modules . Lecture Notes in Math. Volume 1634 . Berlin-Heidelberg-New York : Springer-Verlag .
- Communicated by Q. Wu.