1. Introduction
Throughout this article,
G will be a group with identity
e and
R a commutative ring with nonzero unity 1. Then
R is said to be
G-graded if
with
for all
where
is an additive subgroup of
R for all
. The elements of
are called homogeneous of degree
g. If
, then
x can be written uniquely as
, where
is the component of
x in
. It is known that
is a subring of
R and
. The set of all homogeneous elements of
R is
. Assume that
M is a left unitary
R-module. Then
M is said to be
G-graded if
with
for all
where
is an additive subgroup of
M for all
. The elements of
are called homogeneous of degree
g. It is clear that
is an
-submodule of
M for all
. If
, then
x can be written uniquely as
, where
is the component of
x in
. The set of all homogeneous elements of
M is
. Let
K be an
R-submodule of a graded
R-module
M. Then
K is said to be graded
R-submodule if
, i.e., for
,
where
for all
. An
R-submodule of a graded
R-module need not be graded. For more details and terminology, see [
1,
2].
Specifically,
turns out to be a graded ideal of
R. May
I be an ideal of
R, rightly graded. Then the graded radical of
I will be
, and is defined to be the collection of all
so that for every
, there exists
for which
. One can see that if
, then
if and only if
for some
. In fact,
is a graded ideal of
R, see [
3]. Let
K be a graded
R-submodule of
M. The graded radical of
K is then denoted by
and is specified as the intersection of all graded prime submodules of
M enclosing
K. If no graded prime submodule contains
K exists, we can take
.
A graded prime (resp. graded primary)
R-submodule is a graded
R-submodule
with the property that for
and
such that
implies that
or
(resp.
or
. As graded prime ideals (submodules) have an important role in graded ring (module) theory, several authors generalized these concepts in different ways, see ([
4,
5,
6,
7,
8]). Atani in [
9] has introduced graded weakly prime submodules. A graded
R-submodule
is called graded weakly prime if whenever
and
with
, then
or
. The concept of graded
-prime submodules has been introduced in [
10]. Let
be a function, where
denotes the collection of graded submodules of
M. A graded
R-submodule
is called graded
-prime if whenever
and
such that
, then
or
.
Graded 2-absorbing ideals (resp. graded weakly 2-absorbing ideals) are introduced in [
11] as a different generalization of graded prime ideals (resp. graded weakly prime ideals). A proper graded ideal
I of
R is a graded 2-absorbing ideal (resp. graded weakly 2-absorbing ideal) of
R if whenever
and
(resp.
), then
or
or
. Then introducing graded 2-absorbing submodules (resp. graded weakly 2-absorbing submodules) in [
5] generalized the concept of graded 2-absorbing ideals (resp. graded weakly 2-absorbing ideals) to graded submodules.
Al-Zoubi and Sharafat in [
12] proposed the notion of graded 2-absorbing primary ideals, where a proper graded ideal
I of
R is called graded 2-absorbing primary if whenever
with
, then
or
or
. The notion of graded 2-absorbing primary submodules is studied in [
7] as a generalization of graded 2-absorbing primary ideals. A proper graded
R-submodule
K of
M is said to be a graded 2-absorbing primary
R-submodule (resp. graded weakly 2-absorbing primary
R-submodule) of
M if whenever
and
with
(resp.
), then
or
or
.
A graded
R-module
M is called a graded multiplication if for any graded
R-submodule
K, there exists a graded ideal
I of
R with
. In this instance,
. Graded multiplication modules were firstly introduced by Escoriza and Torrecillas in [
13], and further results were obtained by several authors, see for example [
14]. Let
N and
K be graded
R-submodules of a graded multiplication
R-module
M with
and
for some graded ideals
I and
J of
R. The product of
N and
K is denoted by
is defined by
. Then the product of
N and
K is independent of presentations of
N and
K. In fact, as
is a graded ideal of
R (see [
2]),
is a graded
R-submodule of
M and
. Moreover, for
, by
, we mean the product of
and
. Also, it can be seen in ([
8], Theorem 9) that if
N is a proper graded
R-submodule of a graded multiplication
R-module
M, then
.
In this article, our aim is to extend the notion of graded 2-absorbing submodules to graded
-2-absorbing submodules using similar techniques to that are used in [
10], and also to extend graded 2-absorbing primary submodules to graded
-2-absorbing primary submodules. Our study is inspired by [
15].
2. Graded -2-Absorbing and Graded -2-Absorbing Primary Submodules
This segment includes proposing and examining the notions of graded -2-absorbing and graded -2-absorbing primary submodules.
Definition 1. Let M be a G-graded R-module and be a function.
- 1.
A graded R-submodule is called graded ϕ-primary submodule if whenever and with , then or .
- 2.
A graded R-submodule K with for some is called g-ϕ-primary submodule if whenever and with , then or .
- 3.
A graded R-submodule is called graded ϕ-2-absorbing submodule (ϕ-2-abs. submodule) if whenever and with , then or or .
- 4.
A graded R-submodule K with for some is called g-ϕ-2-absorbing submodule (g-ϕ-2-abs. submodule) if whenever and with , then or or .
- 5.
A graded R-submodule of M is called graded ϕ-2-absorbing primary submodule (ϕ-2-abs. prim. submodule) if whenever and with , then or or .
- 6.
A graded R-submodule K with for some is called g-ϕ-2-absorbing primary submodule (g-ϕ-2-abs. prim. submodule) if whenever and with , then or or .
- 7.
A proper graded R-submodule K of M is said to be a graded ϕ-almost primary R-submodule of M if whenever and such that , then either or .
Remark 1. - 1.
For a graded ϕ-primary R-submodule K of a graded multiplication R-module M, we have the following functions:
graded primary submodule,
graded weakly primary submodule,
graded almost primary submodule,
graded n-almost primary submodule, and
graded ω-primary submodule.
- 2.
Let K be a graded ϕ-2-abs. R-submodule (resp. graded ϕ-2-abs. prim. R-submodule) of a graded multiplication R-module M. Then
graded 2-abs. submodule (resp. graded 2-abs. prim. submodule),
graded weakly 2-abs. submodule (resp. graded weakly 2-abs. prim. submodule),
graded almost 2-abs. submodule (resp. graded almost 2-abs. prim. submodule),
graded n-almost 2-abs. submodule (resp. graded n-almost 2-abs. prim. submodule), and
graded ω-2-abs. submodule (resp. graded ω-2-abs. prim. submodule).
- 3.
For functions , we write if for all . Obviously, therefore, we have the next order:
.
- 4.
If , then every graded ϕ-2-abs. submodule (resp. graded ϕ-2-abs. prim. submodule) is graded ψ-2-abs. submodule (resp. graded ψ-2-abs. prim.submodule).
Remark 2. Since for any graded R-submodule K, we may assume without loss of generality, and we will do so throughout this article.
Theorem 1. Let M be a graded R-module and K be a proper graded R-submodule of M. Then the following implications hold:
- 1.
K is graded ϕ-prime submodule ⇒K is graded ϕ-2-abs. submodule ⇒K is graded ϕ-2-abs. prim. submodule.
- 2.
If M is a graded multiplication R-module and K is a graded ϕ-primary submodule, then K is graded ϕ-2-abs. prim. submodule
- 3.
For graded multiplication R-module M, K is graded 2-abs. submodule ⇒K is graded weakly 2-abs. submodule ⇒K is graded ω-2-abs. submodule ⇒K is graded -almost 2-abs. submodule ⇒K is graded n-almost 2-abs. submodule for all ⇒K is graded almost 2-abs. submodule.
- 4.
For graded multiplication R-module M, K is graded 2-abs. prim. submodule ⇒K is graded weakly 2-abs. prim. submodule ⇒K is graded ω-2-abs. prim. submodule ⇒K is graded -almost 2-abs. prim. submodule ⇒K is graded n-almost 2-abs. prim. submodule for all ⇒K is graded almost 2-abs. prim. submodule.
- 5.
Suppose that . Then K is graded ϕ-2-abs. prim. submodule if and only if K is graded ϕ-2-abs. submodule.
- 6.
If M is a graded multiplication R-module and K is an idempotent graded R-submodule of M, then K is graded ω-2-abs. submodule, and K is graded n-almost 2-abs. submodule for every .
- 7.
Let M be a graded multiplication R-module. Then K is graded n-almost 2-abs. submodule (resp. graded n-almost 2-abs. prim. submodule) for all if and only if K is graded ω-2-abs. submodule (resp. graded ω-2-abs. prim. submodule).
Proof. This is straightforward.
Let and with . suppose that . Then and then as K is a graded -primary R-submodule. Therefore, . Consequently, K is graded -2-absorbing primary.
This is clear by Remark 1 (4).
This is clear by Remark 1 (4).
The claim is obvious.
Since K is an idempotent R-submodule, for all , and then . Thus K is a graded -2-abs.. By (3), we conclude that K is a graded n-almost 2-abs. for all .
Suppose that K is a graded n-almost 2-absorbing (resp. graded n-almost 2-absorbing primary) R-submodule of M for all . Let and with but . Hence for some . Since K is graded n-almost 2-abs. (resp. graded n-almost 2-abs. prim.) for all , this implies either or or (resp. or or ). This completes the first implication. The converse is clear from (3) (resp. from (4)).
□
Proposition 1. Let M be a graded R-module and K be a graded ϕ-2-abs. prim. submodule of M. If is a graded 2-abs. prim. submodule of M, then K is a graded-2-abs. prim. submodule of M.
Proof. Let and such that . If , then we conclude that or or since is graded 2-abs. prim., and so the result holds. If , then the result holds easily since K is graded -2-abs. prim. submodule. □
Theorem 2. Let M be a graded R-module and K be a graded R-submodule of M with . If is a graded ϕ-prime submodule of M, then K is a graded ϕ-2-abs. prim. submodule of M.
Proof. Let and with and . Because is a graded -prime and , . So, . Consequently, K is a graded -2-abs. prim. of M. □
Next we consider the behaviour of graded
-2-absorbing (primary) submodules under graded quotient modules. Let
M be a
G-graded
R-module and
K be a graded
R-submodule of
M. Then
is
G-graded by
for all
([
2]).
Lemma 1 ([
16], Lemma 3.2)
. Let M be a graded R-module, K be a graded R-submodule of M, and N be an R-submodule of M such that . Then N is a graded R-submodule of M if and only if is a graded R-submodule of . Theorem 3. Let M be a graded R-module and K be a proper graded R-submodule of M.
- 1.
K is a graded ϕ-2-abs. submodule of M if and only if is a graded weakly 2-abs. submodule of .
- 2.
K is a graded ϕ-2-abs. prim. submodule of M if and only if is a graded weakly 2-abs. prim. submodule of .
- 3.
K is a graded ϕ-prime submodule of M if and only if is a graded weakly prime submodule of .
- 4.
K is a graded ϕ-primary submodule of M if and only if is a graded weakly primary submodule of .
Proof. Let and with . Then such that , but . Hence or or . So, or or , as desired. Conversely, let and such that and . Then with . Hence or or . So, or or . Thus K is a graded -2-abs.submodule.
Let and with . Then with , but . Hence either or or . So, or or . The result holds since . One can easily prove the converse.
One can easily prove (3) and (4) along the same lines. □
Next we consider the behaviour of graded
-2-absorbing (primary) submodules under graded homomorphisms. Let
M and
L be two
G-graded
R-modules. An
R-homomorphism
is said to be a graded
R-homomorphism if
for all
([
2]).
Lemma 2. ([
4], Lemma 2.16)
. Suppose that is a graded R-homomorphism. If N is a graded R-submodule of L, then is a graded R-submodule of M. Lemma 3 ([
17], Lemma 4.8)
. Suppose that is a graded R-homomorphism. If K is a graded R-submodule of M, then is a graded R-submodule of . Theorem 4. Suppose that is a graded R-epimorphism. Let and be functions.
- 1.
If N is a graded ψ-2-abs. prim. submodule of L and , then is a graded ϕ-2-abs. prim. of M.
- 2.
If K is a graded ϕ-2-abs. prim. submodule of M containing and , then is a graded ψ-2-abs. prim. submodule of L.
- 3.
If N is a graded ψ-2-abs. submodule of L and , then is a graded ϕ-2-abs. submodule of M.
- 4.
If K is a graded ϕ-2-abs. submodule of M containing and , then is a graded ψ-2-abs. submodule of L.
Proof. Since
f is epimorphism,
is proper. Let
and
with
and
. Since
,
. Also,
implies that
. Thus
. Then
or
or
. Thus
or
or
. Since
([
18], Theorem 2.16), we should conclude that
is a graded
-2-abs. prim. submodule.
Let and with . Because f is a graded epimorphism, there is with . Hence, and so as . Because , we have . Hence . It implies that or or . Thus or or . As implies , we are done.
One can easily prove (3) and (4) along the same lines. □
Next we consider the behaviour of graded
-2-absorbing (primary) submodules under multiplicative homogeneous set. Let
M be a
G-graded
R-module and
be a multiplicative set. Then
is a
G-graded
-module with
for all
, and
for all
. If
K is a graded
R-submodule of
M, then
is a graded
-submodule of
. Let
be a function and define
by
for
and
otherwise, for every graded
R-submodule
K of
M ([
10]).
Theorem 5. Let M be a graded R-module and be a multiplicative set.
- 1.
If K is a graded ϕ-2-abs. prim. of M and , then is a graded -2-abs. prim. of .
- 2.
If K is a graded ϕ-2-abs. of M and , then is a graded -2-abs. of .
Proof. 1. Let and with . Then and with for some , and then or or . So, or or .
Similarly, one can easily prove (2). □
Next we consider the behaviour of graded
-2-absorbing (primary) submodules under graded Cartesian product. Let
be a
G-graded
-module,
be a
G-graded
-module and
. Then
is a
G-graded
R-module with
for all
, where
for all
([
2]).
Lemma 4 ([
16], Lemma 3.12)
. Let be a G-graded -module, be a G-graded -module, and . Then is a graded R-submodule of M if and only if N is a graded -submodule of and K is a graded -submodule of . Lemma 5. Let be a G-graded -module, be a G-graded -module, and . Suppose that , be functions and . Assume that for some proper graded -submodule of . If K is a graded ϕ-2-abs. submodule of M, then is a graded -2-abs. submodule of .
Proof. Let and with . Then for with the same degree as , respectively, and for with the same degree as , and with . Since K is a graded -2-abs. submodule of M, we get either or or . So clearly, we conclude that or or . Therefore, is a graded -2-abs. submodule of . □
Theorem 6. Let be a G-graded -module, be a G-graded -module, and . Suppose that , be functions and . Assume that for some proper graded -submodule of .
- 1.
If , then K is a graded ϕ-2-abs. submodule of M if and only if is a graded -2-abs. submodule of .
- 2.
If , then K is a graded ϕ-2-abs. submodule of M if and only if is a graded 2-abs. submodule of .
Proof. Suppose that is a graded -2-abs. submodule of . Let and with . Since , we get that and with , and this implies that or or . Thus either or or . Hence, K is a graded -2-abs. submodule of M. The converse holds from Lemma 5.
Suppose that
K is a graded
-2-abs. submodule of
M. Since
, there is
and then there is
with
. Suppose that
is not a graded 2-abs. of
. By Lemma 5,
is a graded
-2-abs. of
. Hence, there are
and
with
,
,
and
. So,
which implies that
or
or
, that is a contradiction. So,
is a graded 2-abs. submodule of
. Conversely, if
is a graded 2-abs. submodule of
, then
is a graded 2-abs. submodule of
M by ([
6], Theorem 3.3). Hence
K is a graded
-2-abs. submodule of
M for any
.
□
Lemma 6. Let be a G-graded -module, be a G-graded -module, and . Suppose that , be functions and . Assume that for some proper graded -submodule of . If K is a graded ϕ-2-abs. prim. submodule of M, then is a graded -2-abs. prim. submodule of .
Proof. The proof uses the same procedure in Lemma 5. □
Theorem 7. Let be a G-graded -module, be a G-graded -module, and . Suppose that , be functions and . Assume that for some proper graded -submodule of .
- 1.
If , then K is a graded ϕ-2-abs. prim. submodule of M if and only if is a graded -2-abs. prim. submodule of .
- 2.
If , then K is a graded ϕ-2-abs. prim. submodule of M if and only if is a graded 2-abs. prim. submodule of .
3. More Results
In this section, we introduce more results concerning the g-components of M, .
Theorem 8. Let M be a G-graded R-module and K be a g-ϕ-primary submodule of M. Suppose that and such that , and . Then
- 1.
.
- 2.
.
- 3.
.
Proof. Suppose that . Then there is with , and then . Since and , we deduce that as K is a g--primary R-submodule of M. So , which is a contradiction. So, .
Suppose that . Then there is with , and then as . Since , we get . Since , so . Hence , which is a contradiction.
Suppose that . Then there exist and such that . By (1) and (2), . So, either or . Thus we have either or , which is a contradiction.
□
Remark 3. Note that if K is a g-ϕ-primary submodule of M which is not g-primary, then there are and with , and . So, every g-ϕ-primary submodule, which is not g-primary, satisfies the assumptions of Theorem 8.
Theorem 9. Let M be a G-graded R-module, and K be a g-ϕ-2-abs. submodule of M. Suppose that and with , , and . Then
- 1.
.
- 2.
.
- 3.
.
- 4.
.
Proof. Suppose that . Then there is with , and then . Since and , we conclude that or . So, or , which is a contradiction. Thus .
Suppose that . Then there is with , and then as . Since , we obtain that . Then or or . Hence or or , which is a contradiction. Hence, .
It can be easily proved by using a similar procedure in part (2).
Assume that . Then there exist with , and then by parts (2) and (3), . Clearly, . Then or or . Therefore, or or , which is a contradiction. Consequently, .
□
Remark 4. Note that if K is a g-ϕ-2-abs. submodule of M which is not g-2-abs., then there are and with , , and . So, every g-ϕ-2-abs. submodule, which is not g-2-abs., satisfies the assumptions of Theorem 9.
Theorem 10. Let M be a G-graded R-module, and K be a g-ϕ-2-abs. prim. submodule of M. Consider and with , , and . Then
- 1.
.
- 2.
.
- 3.
.
- 4.
.
Proof. This can be easily proved in a similar way as Theorem 9. □
Remark 5. Note that if K is a g-ϕ-2-abs. prim. submodule of M which is not g-2-abs. prim., then there are and with , , and . So, every g-ϕ-2-abs. prim. submodule, which is not g-2-abs. prim., satisfies the assumptions of Theorem 10.
Theorem 11. Let M be a G-graded R-module and . If K is a g-ϕ-2-abs. prim. submodule of M that is not g-2-abs. prim., then .
Proof. Since K is a g--2-abs. prim. submodule of M that is not g-2-abs. prim., there are and such that , , and . Suppose that . Then there are and such that . By Theorem 10, we get . So, or or . Therefore, or or , which is a contradiction. Hence, . □