This paper,combined algebraical structure with analytical system,has studied the part of theory of C~*-modules over A by using the homolgical methods, where A is a commutative C~*-algebra over complex number field C. ...This paper,combined algebraical structure with analytical system,has studied the part of theory of C~*-modules over A by using the homolgical methods, where A is a commutative C~*-algebra over complex number field C. That is to say we have not only defined some relevant new concept,but also obtained some results about them.展开更多
In this note, we establish a new characterization on g-frames in Hilbert C;-modules from the operator-theoretic point of view, with which we provide a correction to one result recently obtained by Yao(Yao X Y. Some pr...In this note, we establish a new characterization on g-frames in Hilbert C;-modules from the operator-theoretic point of view, with which we provide a correction to one result recently obtained by Yao(Yao X Y. Some properties of g-frames in Hilbert C;-modules(in Chinese). Acta Math. Sinica, 2011, 54(1): 1–8.).展开更多
In this article, we introduce the notion of generalized derivations on Hilbert C*-modules. We use a fixed-point method to prove the generalized Hyers-Ulam-Rassias stability associated to the Pexiderized Cauchy-Jensen...In this article, we introduce the notion of generalized derivations on Hilbert C*-modules. We use a fixed-point method to prove the generalized Hyers-Ulam-Rassias stability associated to the Pexiderized Cauchy-Jensen type functional equationrf(x+y/r)+sg(x-y/s)=2h(x)for r, s ∈ R / {0} on Hilbert C*-modules, where f, g, and h are mappings from a Hilbert C*-module M to M.展开更多
Let R be a Noetherian ring. The projectivity and injectivity of modules over R are discussed. The concept of modules is introduced and the descriptions for co-*-modules over R are given. At last, cotilting modules ove...Let R be a Noetherian ring. The projectivity and injectivity of modules over R are discussed. The concept of modules is introduced and the descriptions for co-*-modules over R are given. At last, cotilting modules over R are characterized by means of co-*-modules.展开更多
Theory of uncertainty reasoning base on l-module of true value field,in this paper,an extended l-module was proposed,some properties and lattice measure were discussed,then the lattice integral on l-module was gained.
A module is called a co-*∞-module if it is co-selfsmall and ∞-quasi-injective. The properties and characterizations are investigated. When a module U is a co-*∞-module, the functor Hom RU(-,U)is exact in Copre...A module is called a co-*∞-module if it is co-selfsmall and ∞-quasi-injective. The properties and characterizations are investigated. When a module U is a co-*∞-module, the functor Hom RU(-,U)is exact in Copres∞(U). A module U is a co-*∞-module if and only if U is co-selfsmall and for any exact sequence 0→M→UI→N→0 with M∈Copres∞(U) and I is a set, N∈Copres∞(U) is equivalent to Ext1R(N,U)→Ext1R(UI,U) is a monomorphism if and only if U is co-selfsmall and for any exact sequence 0→L→M→N→0 with L, N∈Copres∞(U), N∈Copres∞(U) is equivalent to the induced sequence 0→Δ(N)→Δ(M)→Δ(L)→0 which is exact if and only if U induces a duality ΔUS:⊥USCopres∞(U):ΔRU. Moreover, U is a co-*n-module if and only if U is a co-*∞-module and Copres∞(U)=Copresn(U).展开更多
We characterize A-linear symmetric and contraction module operator semigroup{Tt}t∈R+L(l2(A)),where A is a finite-dimensional C-algebra,and L(l2(A))is the C-algebra of all adjointable module maps on l2(A).Next,we intr...We characterize A-linear symmetric and contraction module operator semigroup{Tt}t∈R+L(l2(A)),where A is a finite-dimensional C-algebra,and L(l2(A))is the C-algebra of all adjointable module maps on l2(A).Next,we introduce the concept of operator-valued quadratic forms,and give a one to one correspondence between the set of non-positive definite self-adjoint regular module operators on l2(A)and the set of non-negative densely defined A-valued quadratic forms.In the end,we obtain that a real and strongly continuous symmetric semigroup{Tt}t∈R+L(l2(A))being Markovian if and only if the associated closed densely defined A-valued quadratic form is a Dirichlet form.展开更多
Let M be a full Hilbert C*-module over a C*-algebra A, and let End^(.A4) be the algebra of adjointable operators on M. We show that if A is unital and commutative, then every derivation of End*A(M) is an inner ...Let M be a full Hilbert C*-module over a C*-algebra A, and let End^(.A4) be the algebra of adjointable operators on M. We show that if A is unital and commutative, then every derivation of End*A(M) is an inner derivation, and that if A is a-unital and commutative, then innerness of derivations on "compact" operators completely decides innerness of derivations on EndA(M). If .4 is unital (no commutativity is assumed) such that every derivation of A is inner, then it is proved that every derivation of EndA(Ln(A)) is also inner, where Ln(A) denotes the direct sum of n copies of A. In addition, in case A is unital, commutative and there exist xo,yo ∈M such that 〈xo,yo〉 = 1, we characterize the linear A-module homomorphisms on EndA(M) which behave like derivations when acting on zero products.展开更多
In this paper,we focus on combining the theories of fuzzy soft sets with Γ-modules,and establishing a new framework for fuzzy soft Γ-submodules.The main contributions of the paper are 3-fold.First,we present the con...In this paper,we focus on combining the theories of fuzzy soft sets with Γ-modules,and establishing a new framework for fuzzy soft Γ-submodules.The main contributions of the paper are 3-fold.First,we present the concepts of(R,S)-bi-Γ-submodules,quasi-Γ-submodules and regular Γ-modules.Meanwhile,some illustrative examples are given to show the rationality of the definitions introduced in this paper.Second,several new kinds of generalized fuzzy soft Γ-submodules are proposed,and related properties and mutual relationships are also investigated.Third,we discover some intrinsic connections between the generalized fuzzy soft Γ-submodules presented in this paper and crisp Γ-submodules,and describe the relationships between regular Γ-modules and the generalized fuzzy soft Γ-submodules presented in this paper.展开更多
In this paper we define and study chain conditions for Hilbert C*-modules through their C*-algebras of compact operators and discuss their perseverance under Morita equivalence and tensor products. We show that thes...In this paper we define and study chain conditions for Hilbert C*-modules through their C*-algebras of compact operators and discuss their perseverance under Morita equivalence and tensor products. We show that these chain conditions are passed from the C*-algebra to its Hilbert module under certain conditions. We also study chain conditions for Hilbert modules coming from inclusion of C*-algebra with a faithful conditional expectation.展开更多
Let E be a Hilbert C*-module,and Y be an orthogonally complemented closed submodule of E.The authors generalize the definitions of Y-complementability and Y-compatibility for general(adjointable) operators from Hil...Let E be a Hilbert C*-module,and Y be an orthogonally complemented closed submodule of E.The authors generalize the definitions of Y-complementability and Y-compatibility for general(adjointable) operators from Hilbert space to Hilbert C*-module,and discuss the relationship between each other.Several equivalent statements about Y-complementability and Y-compatibility,and several representations of Schur complements of Y-complementable operators(especially,of Y-compatible operators and of positive Y-compatible operators) on a Hilbert C*-module are obtained.In addition,the quotient property for Schur complements of matrices is generalized to the quotient property for Schur complements of Y-complementable operators and Y*-complementable operators on a Hilbert C*-module.展开更多
In the paper, we introduce weak Bessel sequences and weak frames in a Hilbert C*-module 74, and give a characterization of weak Bessel sequences, weak frames, normalized tight weak frames, and dual weak frames to eac...In the paper, we introduce weak Bessel sequences and weak frames in a Hilbert C*-module 74, and give a characterization of weak Bessel sequences, weak frames, normalized tight weak frames, and dual weak frames to each other, respectively. Using .A-valued linear bounded operator U : H → l^2(.A), V*U = I, a coustructing method of dual weak frame {xj^* : j ∈ H} for a given weak frame {Xj : j ∈ J} is obtained. Moreover, pseudo frame decompositions for 74 is given.展开更多
The notion of weak Doi-Hopfπ-datum and weak Doi-Hopfπ-module are given as generalizations of an ordinary weak Doi-Hopf datum and weak Doi-Hopf module introduced in (Boehm, 2000), also as a generalization of a Doi-...The notion of weak Doi-Hopfπ-datum and weak Doi-Hopfπ-module are given as generalizations of an ordinary weak Doi-Hopf datum and weak Doi-Hopf module introduced in (Boehm, 2000), also as a generalization of a Doi-Hopfπ-module introduced in (Wang, 2004). Then we also show that the functor forgetting action or coaction has an adjoint. Furthermore we explain how the notion of weak Doi-Hopfπ-datum is related to weak smash product. This paper presents our preliminary results on weak Doi-Hopf group modules.展开更多
It’s created a canonical Lie algebra in electrodynamics with all the “nice” algebraic and geometrical properties of an universal enveloping algebra with the goal of can to obtain generalizations in quantum electrod...It’s created a canonical Lie algebra in electrodynamics with all the “nice” algebraic and geometrical properties of an universal enveloping algebra with the goal of can to obtain generalizations in quantum electrodynamics theory of the TQFT, and the Universe based in lines and twistor bundles to the obtaining of irreducible unitary representations of the Lie groups SO(4) ?andO(3,1) , based in admissible representations of U(1) , and SU(n)? . The obtained object haves the advantages to be an algebraic or geometrical space at the same time. This same space of £-modules can explain and model different electromagnetic phenomena in superconductor and quantum processes where is necessary an organized transformation of the electromagnetic nature of the space- time and obtain nanotechnologies of the space-time and their elements.展开更多
In this paper, we obtain the boundedness of the fractional integral operators, the bilineax fractional integral operators and the bilinear Hilbert transform on α-modulation spaces.
Motivated by two norm equations used to characterize the Friedrichs angle,this paper studies C^(*)-isomorphisms associated with two projections by introducing the matched triple and the semi-harmonious pair of project...Motivated by two norm equations used to characterize the Friedrichs angle,this paper studies C^(*)-isomorphisms associated with two projections by introducing the matched triple and the semi-harmonious pair of projections.A triple(P,Q,H)is said to be matched if is a Hilbert C^(*)-module,P and Q are projections on H such that their infimum P∧Q exists as an element of L(H),where L(H)denotes the set of all adjointable operators on H.The C^(*)-sub algebras of L(H)generated by elements in{P-P∧Q,Q-P∧Q,I}and{P,Q,P∧Q,I}are denoted by i(P,Q,H)and o(P,Q,H),respectively.It is proved that each faithful representation(π,X)of o(P,Q,H)can induce a faithful representation(π,X)of i(P,Q,H)such that π~(P−P∧Q)=π(P)−π(P)∧π(Q),π~(Q−P∧Q)=π(Q)−π(P)∧π(Q)..When(P,Q)is semi-harmonious,that is,R(P+Q) and R(2I−P−Q) are both orthogonally complemented in H,it is shown that i(P,Q,H)and i(I-Q,I-P,H)are unitarily equivalent via a unitary operator in L(H).A counterexample is constructed,which shows that the same may be not true when(P,Q)fails to be semi-harmonious.Likewise,a counterexample is constructed such that(P,Q)is semi-harmonious,whereas(P,I-Q)is not semi-harmonious.Some additional examples indicating new phenomena of adjointable operators acting on Hilbert C^(*)-modules are also provided.展开更多
In this paper,we generalize the Takesaki-Takai duality theorem in Hilbert C~*-modules; that is to say,if (H,V,U) is a Kac-system,where H is a Hilbert space,V is a multiplicative unitary operator on H(?)H and U is a un...In this paper,we generalize the Takesaki-Takai duality theorem in Hilbert C~*-modules; that is to say,if (H,V,U) is a Kac-system,where H is a Hilbert space,V is a multiplicative unitary operator on H(?)H and U is a unitary operator on H,and if E is an (?)-compatible Hilbert (?)-module, then E×(?)×(?)K(H),where K(H) is the set of all compact operators on H,and (?) and (?) are Hopf C~*-algebras corresponding to the Kac-system (H,V,U).展开更多
The notion of operator-valued free Fisher information was introduced.It is a generalization of free Fisher information which was defined by D.Voiculescu on tracial von Neumann algebras.It is proved that the operator-v...The notion of operator-valued free Fisher information was introduced.It is a generalization of free Fisher information which was defined by D.Voiculescu on tracial von Neumann algebras.It is proved that the operator-valued free Fisher information is closely related to amalgamated freeness,i.e.,the operator-valued free Fisher information of some random variables is additive if and only if these random variables are a free family with amalgamation over a subalgebra.Cramer-Rao inequality in operator-valued settings is also obtained.展开更多
By discussing equivalence between Copres(K A) and Gen(P R), the characterization of *-modules was presented. The characterization of the duality between Cogen(U R) and Cogen( AU) was also discussed.
One of the continuity conditions identified by Utumi on self-injective rings is the C3-condition, where a module M is called a C3-module if whenever A and B are direct summands of M and A A B = 0, then A B is a summa...One of the continuity conditions identified by Utumi on self-injective rings is the C3-condition, where a module M is called a C3-module if whenever A and B are direct summands of M and A A B = 0, then A B is a summand of M. In addition to injective and direct-injective modules, the class of C3-modules includes the semisimple, continuous, indecomposable and regular modules. Indeed, every commutative ring is a C3-ring. In this paper we provide a general and unified treatment of the above mentioned classes of modules in terms of the C3-condition, and establish new characterizations of several well known classes of rings.展开更多
文摘This paper,combined algebraical structure with analytical system,has studied the part of theory of C~*-modules over A by using the homolgical methods, where A is a commutative C~*-algebra over complex number field C. That is to say we have not only defined some relevant new concept,but also obtained some results about them.
基金The NSF(11271148,11561057)of Chinathe NSF(20151BAB201007)of Jiangxi Provincethe Science and Technology Project(GJJ151061)of Jiangxi Education Department
文摘In this note, we establish a new characterization on g-frames in Hilbert C;-modules from the operator-theoretic point of view, with which we provide a correction to one result recently obtained by Yao(Yao X Y. Some properties of g-frames in Hilbert C;-modules(in Chinese). Acta Math. Sinica, 2011, 54(1): 1–8.).
文摘In this article, we introduce the notion of generalized derivations on Hilbert C*-modules. We use a fixed-point method to prove the generalized Hyers-Ulam-Rassias stability associated to the Pexiderized Cauchy-Jensen type functional equationrf(x+y/r)+sg(x-y/s)=2h(x)for r, s ∈ R / {0} on Hilbert C*-modules, where f, g, and h are mappings from a Hilbert C*-module M to M.
文摘Let R be a Noetherian ring. The projectivity and injectivity of modules over R are discussed. The concept of modules is introduced and the descriptions for co-*-modules over R are given. At last, cotilting modules over R are characterized by means of co-*-modules.
基金Supported by NSF of the Education Department of Henan Province(2009A110017)
文摘Theory of uncertainty reasoning base on l-module of true value field,in this paper,an extended l-module was proposed,some properties and lattice measure were discussed,then the lattice integral on l-module was gained.
基金The National Natural Science Foundation of China (No.10971024)Specialized Research Fund for the Doctoral Program of Higher Education (No.200802860024)
文摘A module is called a co-*∞-module if it is co-selfsmall and ∞-quasi-injective. The properties and characterizations are investigated. When a module U is a co-*∞-module, the functor Hom RU(-,U)is exact in Copres∞(U). A module U is a co-*∞-module if and only if U is co-selfsmall and for any exact sequence 0→M→UI→N→0 with M∈Copres∞(U) and I is a set, N∈Copres∞(U) is equivalent to Ext1R(N,U)→Ext1R(UI,U) is a monomorphism if and only if U is co-selfsmall and for any exact sequence 0→L→M→N→0 with L, N∈Copres∞(U), N∈Copres∞(U) is equivalent to the induced sequence 0→Δ(N)→Δ(M)→Δ(L)→0 which is exact if and only if U induces a duality ΔUS:⊥USCopres∞(U):ΔRU. Moreover, U is a co-*n-module if and only if U is a co-*∞-module and Copres∞(U)=Copresn(U).
基金supported by the Fundamental Research Funds for the Central Universitiesthe Research Funds of Remin University of China(Grant No.10XNJ033)
文摘We characterize A-linear symmetric and contraction module operator semigroup{Tt}t∈R+L(l2(A)),where A is a finite-dimensional C-algebra,and L(l2(A))is the C-algebra of all adjointable module maps on l2(A).Next,we introduce the concept of operator-valued quadratic forms,and give a one to one correspondence between the set of non-positive definite self-adjoint regular module operators on l2(A)and the set of non-negative densely defined A-valued quadratic forms.In the end,we obtain that a real and strongly continuous symmetric semigroup{Tt}t∈R+L(l2(A))being Markovian if and only if the associated closed densely defined A-valued quadratic form is a Dirichlet form.
基金supported by National Natural Science Foundation of China(Grant No.11171151)Natural Science Foundation of Jiangsu Province of China(Grant No.BK2011720)supported by Singapore Ministry of Education Academic Research Fund Tier1(Grant No.R-146-000-136-112)
文摘Let M be a full Hilbert C*-module over a C*-algebra A, and let End^(.A4) be the algebra of adjointable operators on M. We show that if A is unital and commutative, then every derivation of End*A(M) is an inner derivation, and that if A is a-unital and commutative, then innerness of derivations on "compact" operators completely decides innerness of derivations on EndA(M). If .4 is unital (no commutativity is assumed) such that every derivation of A is inner, then it is proved that every derivation of EndA(Ln(A)) is also inner, where Ln(A) denotes the direct sum of n copies of A. In addition, in case A is unital, commutative and there exist xo,yo ∈M such that 〈xo,yo〉 = 1, we characterize the linear A-module homomorphisms on EndA(M) which behave like derivations when acting on zero products.
基金Supported by the National Natural Science Foundation of China (61175055)the Innovation Term of Higher Education of Hubei Province,China (T201109)+1 种基金the Natural Science Foundation of Hubei Province (2012FFB01101)the Natural Science Foundation of Education Committee of Hubei Province (D20131903)
文摘In this paper,we focus on combining the theories of fuzzy soft sets with Γ-modules,and establishing a new framework for fuzzy soft Γ-submodules.The main contributions of the paper are 3-fold.First,we present the concepts of(R,S)-bi-Γ-submodules,quasi-Γ-submodules and regular Γ-modules.Meanwhile,some illustrative examples are given to show the rationality of the definitions introduced in this paper.Second,several new kinds of generalized fuzzy soft Γ-submodules are proposed,and related properties and mutual relationships are also investigated.Third,we discover some intrinsic connections between the generalized fuzzy soft Γ-submodules presented in this paper and crisp Γ-submodules,and describe the relationships between regular Γ-modules and the generalized fuzzy soft Γ-submodules presented in this paper.
文摘In this paper we define and study chain conditions for Hilbert C*-modules through their C*-algebras of compact operators and discuss their perseverance under Morita equivalence and tensor products. We show that these chain conditions are passed from the C*-algebra to its Hilbert module under certain conditions. We also study chain conditions for Hilbert modules coming from inclusion of C*-algebra with a faithful conditional expectation.
基金Project supported by the National Natural Science Foundation of China (Nos.10771161,11071188)
文摘Let E be a Hilbert C*-module,and Y be an orthogonally complemented closed submodule of E.The authors generalize the definitions of Y-complementability and Y-compatibility for general(adjointable) operators from Hilbert space to Hilbert C*-module,and discuss the relationship between each other.Several equivalent statements about Y-complementability and Y-compatibility,and several representations of Schur complements of Y-complementable operators(especially,of Y-compatible operators and of positive Y-compatible operators) on a Hilbert C*-module are obtained.In addition,the quotient property for Schur complements of matrices is generalized to the quotient property for Schur complements of Y-complementable operators and Y*-complementable operators on a Hilbert C*-module.
基金Supported by the Emphasis Supported Subject Foundation of Shanxi Province(20055026) Supported by the Emphasis Science Foundation of Yuncheng University(20060103)
文摘In the paper, we introduce weak Bessel sequences and weak frames in a Hilbert C*-module 74, and give a characterization of weak Bessel sequences, weak frames, normalized tight weak frames, and dual weak frames to each other, respectively. Using .A-valued linear bounded operator U : H → l^2(.A), V*U = I, a coustructing method of dual weak frame {xj^* : j ∈ H} for a given weak frame {Xj : j ∈ J} is obtained. Moreover, pseudo frame decompositions for 74 is given.
基金Project supported by the Program for New Century Excellent Talents in University (No. 04-0522), the National Science Foundation of Zhejiang Province of China (No. 102028), and the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (No. 704004)
文摘The notion of weak Doi-Hopfπ-datum and weak Doi-Hopfπ-module are given as generalizations of an ordinary weak Doi-Hopf datum and weak Doi-Hopf module introduced in (Boehm, 2000), also as a generalization of a Doi-Hopfπ-module introduced in (Wang, 2004). Then we also show that the functor forgetting action or coaction has an adjoint. Furthermore we explain how the notion of weak Doi-Hopfπ-datum is related to weak smash product. This paper presents our preliminary results on weak Doi-Hopf group modules.
文摘It’s created a canonical Lie algebra in electrodynamics with all the “nice” algebraic and geometrical properties of an universal enveloping algebra with the goal of can to obtain generalizations in quantum electrodynamics theory of the TQFT, and the Universe based in lines and twistor bundles to the obtaining of irreducible unitary representations of the Lie groups SO(4) ?andO(3,1) , based in admissible representations of U(1) , and SU(n)? . The obtained object haves the advantages to be an algebraic or geometrical space at the same time. This same space of £-modules can explain and model different electromagnetic phenomena in superconductor and quantum processes where is necessary an organized transformation of the electromagnetic nature of the space- time and obtain nanotechnologies of the space-time and their elements.
基金Supported by the National Natural Science Foundation of China(11271330)
文摘In this paper, we obtain the boundedness of the fractional integral operators, the bilineax fractional integral operators and the bilinear Hilbert transform on α-modulation spaces.
基金supported by the National Natural Science Foundation of China(No.11971136)the Science and Technology Commission of Shanghai Municipality(No.18590745200)。
文摘Motivated by two norm equations used to characterize the Friedrichs angle,this paper studies C^(*)-isomorphisms associated with two projections by introducing the matched triple and the semi-harmonious pair of projections.A triple(P,Q,H)is said to be matched if is a Hilbert C^(*)-module,P and Q are projections on H such that their infimum P∧Q exists as an element of L(H),where L(H)denotes the set of all adjointable operators on H.The C^(*)-sub algebras of L(H)generated by elements in{P-P∧Q,Q-P∧Q,I}and{P,Q,P∧Q,I}are denoted by i(P,Q,H)and o(P,Q,H),respectively.It is proved that each faithful representation(π,X)of o(P,Q,H)can induce a faithful representation(π,X)of i(P,Q,H)such that π~(P−P∧Q)=π(P)−π(P)∧π(Q),π~(Q−P∧Q)=π(Q)−π(P)∧π(Q)..When(P,Q)is semi-harmonious,that is,R(P+Q) and R(2I−P−Q) are both orthogonally complemented in H,it is shown that i(P,Q,H)and i(I-Q,I-P,H)are unitarily equivalent via a unitary operator in L(H).A counterexample is constructed,which shows that the same may be not true when(P,Q)fails to be semi-harmonious.Likewise,a counterexample is constructed such that(P,Q)is semi-harmonious,whereas(P,I-Q)is not semi-harmonious.Some additional examples indicating new phenomena of adjointable operators acting on Hilbert C^(*)-modules are also provided.
基金Supported by NSF 10301004,NSF 10171098Yantai University PHD Foundation SX03B14
文摘In this paper,we generalize the Takesaki-Takai duality theorem in Hilbert C~*-modules; that is to say,if (H,V,U) is a Kac-system,where H is a Hilbert space,V is a multiplicative unitary operator on H(?)H and U is a unitary operator on H,and if E is an (?)-compatible Hilbert (?)-module, then E×(?)×(?)K(H),where K(H) is the set of all compact operators on H,and (?) and (?) are Hopf C~*-algebras corresponding to the Kac-system (H,V,U).
文摘The notion of operator-valued free Fisher information was introduced.It is a generalization of free Fisher information which was defined by D.Voiculescu on tracial von Neumann algebras.It is proved that the operator-valued free Fisher information is closely related to amalgamated freeness,i.e.,the operator-valued free Fisher information of some random variables is additive if and only if these random variables are a free family with amalgamation over a subalgebra.Cramer-Rao inequality in operator-valued settings is also obtained.
文摘By discussing equivalence between Copres(K A) and Gen(P R), the characterization of *-modules was presented. The characterization of the duality between Cogen(U R) and Cogen( AU) was also discussed.
文摘One of the continuity conditions identified by Utumi on self-injective rings is the C3-condition, where a module M is called a C3-module if whenever A and B are direct summands of M and A A B = 0, then A B is a summand of M. In addition to injective and direct-injective modules, the class of C3-modules includes the semisimple, continuous, indecomposable and regular modules. Indeed, every commutative ring is a C3-ring. In this paper we provide a general and unified treatment of the above mentioned classes of modules in terms of the C3-condition, and establish new characterizations of several well known classes of rings.