1. Introduction
A topological group structure plays very important role in mathematics, particularly in noncommutative analysis, abstract harmonic analysis and their applications [
1,
2,
3,
4,
5]. Topologies on groupoids, semigroups, other algebraic structures attract great attention. There are also interesting nonassociative metagroups, which appear naturally in noncommutative analysis, noncommutative geometry, operator theory and PDEs. Topological groups are rather well studied, but little is known about their nonassociative analogs, such as topological metagroups and quasigroups. In this article, specific features of topological metagroups and quasigroups are scrutinized.
In particular, analysis of octonions and generalized Cayley–Dickson algebra developed quickly in recent years (see [
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19] and the references therein). It appears that a multiplicative law of their canonical bases is nonassociative and leads to a more general notion of a metagroup instead of a group [
9,
20,
21]. They were used in [
20,
21,
22,
23,
24] for investigations of partial differential operators and other unbounded operators over quaternions and octonions, and also for automorphisms, derivations and cohomologies of generalized
-algebras over
or
C. They certainly have a lot of specific features in their derivations and (co)homology theory [
20,
21]. It was shown in [
24] that an analog of the Stone theorem for one-parameter groups of unitary operators for the generalized
-algebras over quaternions and octonions becomes more complicated and multiparameter. The generalized
-algebras arise naturally, while there are decompositions of PDEs or systems of PDEs of higher orders into PDEs or their systems of order not higher than two [
11,
12,
25,
26], which permits integrating them subsequently or simplifying their analysis.
Recently, nonassociative algebras near to quasigroups were utilized in investigations of slave boson decompositions in superconductors [
27] and in nonassociative quantum mechanics [
28]. They were also actively used in gauge theories and Green–Schwartz superstrings [
29,
30]. Nonassociative algebras of such types are connected with quasi-hopf deformations in nonassociative quantum mechanics [
31]. Nonassociative algebras near to quasigroups served as one of the main tools during studies of De Sitter representations of a curved space-time [
32], in the great unification theory, and for studies of Yang–Mills fields [
12,
33]. The family of such nonassociative algebras was utilized for an analysis of Yang–Baxter PDEs with applications for the great unification theory (see [
34,
35,
36] and the references therein). Quasigroups have found other applications in informatics and coding theory, because they open new opportunities in comparison to groups [
37,
38,
39,
40].
In [
41], different types of products of metagroups were studied such as smashed products and smashed twisted wreath products. Topologies of the smashed twisted wreath products of metagroups were studied in [
42]. There conditions were investigated, providing topological metagroups. Examples were given of large families of topological metagroups in the articles [
41,
42,
43]. That also permitted constructing of their abundant classes, which are different from topological groups. On the other hand, topologies of metagroups and their homomorphisms were not investigated. Their definition is recalled in
Section 1.1.
Notice also that a loop in algebra (i.e., a unital quasigroup) is a quite different object than a loop group considered in geometry or mathematical physics. Note that metagroups are commonly nonassociative, and having many specific features in comparison with groups and quasigroups. On the other hand, if a loop
G is simple, then a subloop generated by all elements of the form
for all
a,
b,
c in
G coincides with
G [
17,
44]. Metagroups are intermediate between groups and quasigroups.
We recall that, according to Chapter 2 and Sections 4.6, 4.10, 4.13 of [
4] and Section 6 of [
3], the compact connected
topological group
G can be presented as the limit of an inverse spectrum (that is, a projective limit of a homomorphism system)
of compact finite-dimensional Lie groups of manifolds over
, where
is a directed set,
is a continuous homomorphism for each
in
,
is the identity map,
for each
,
for each
in
.
This raises questions for a subsequent research. Does a nonassociative analog of a topological group have this property or not? How weak may a nonassociative structure be that does not satisfy this property? This article answers these questions. In it, analogs of topological groups are scrutinized with a rather mild nonassociative metagroup structure.
The methods used by Gleason, Montgomery and Zippin were based on analysis of one-parameter subgroups. In this article, quite different approaches are used. They are based on the previous works of the author, and use smashed twisted wreath products of topological metagroups (see also above). With the help of them the nonassociative analog of the Hilbert’s fifths, the problem for topological metagroups is solved in
Section 2.
In this article topologies on metagroups and quasigroups are studied. They have specific features in comparison with topological groups because of nonassociativity in general of topological metagroups or topological quasigroups. Necessary definitions are recalled. Transversal sets are studied in smashed twisted products of topological metagroups in Theorem 9, and Corollaries 8, 9, and 10. Their inverse spectra are investigated in Theorem 10 and Remark 4. Specific features of the topological quasigroup structures are found in comparison with topological groups and discussed.
1.1. Basic Facts on Metagroups
Necessary facts about metagroups are recalled in this subsection, though a reader familiar with previous works [
41,
42] can skip it.
Definition 1. Let G be a set with a single-valued binary operation (multiplication) defined on G, and satisfying the conditions:
- (i)
For each a and b in G, there is a unique with ;
- (ii)
A unique exists satisfying , which is denoted by and , correspondingly;
- (iii)
There exists a neutral (i.e., unit) element :
for each .
If the set G with a single-valued multiplication satisfies conditions (i) and (ii), then it is called a quasigroup. If the quasigroup G also satisfies condition (iii), then it is called an algebraic loop (or a unital quasigroup or, more shortly, a loop).
The set of all elements commuting and associating with G are:
- (iv)
: = ;
- (v)
: = ;
- (vi)
: = ;
- (vii)
: = ;
- (viii)
: = .
: = is called the center of G.
We call G a metagroup if a set G possesses a single-valued binary operation and satisfies conditions (i)–(iii) and
- (ix)
—for each a, b and c in G, where .
Then, the metagroup G will be called a central metagroup, if it also satisfies the condition:
- (x)
—for each a and b in G, where .
If H is a submetagroup (or a unital subquasigroup) of the metagroup G (or the unital quasigroup G) and
- (xi)
for each , then H will be called almost invariant (or algebraically almost normal). If, in addition,
- (xii)
and , for each g and k in G, then H will be called an invariant (or algebraically normal) submetagroup (or unital subquasigroup, respectively).
Elements of a metagroup G will be denoted by small letters, and subsets of G will be denoted by capital letters. If A and B are subsets in G, then, means the difference of them, . Henceforward, maps and functions of metagroups are supposed to be single-valued, if nothing else is specified.
If is a topology on the metagroup (or quasigroup) G such that multiplication, and are (jointly) continuous from into G, then is called a topological metagroup (or quasigroup, respectively).
Remark 1 ([
41]).
Let A and B be two metagroups and let be a commutative group such thatwhere denotes a minimal subgroup in containing for every a, b and c in A.
Using direct products, it is always possible to extend either A or B to obtain such a case. In particular, either A or B may be a group. On ,
an equivalence relation Ξ is considered such thatfor every v in A, b in B and γ in .
where denotes a family of all bijective surjective single-valued mappings of B onto B, subject to conditions –
given below. If and ,
then it will be written shortly as instead of ,
where .
Also letbe single-valued mappings written shortly as η, κ, and ξ, correspondingly, such thatand κ (u, γ, b) = κ(u, b, γ) = e;andfor every u and v in A, b, c in B, γ in ,
where e denotes the neutral element in and in A and B. We writefor each ,
in A,
and in B. The Cartesian product supplied with such a binary operation will be denoted by .
Then, we writefor each ,
in A ,
and in B.
The Cartesian product supplied with a binary operation will be denoted by .
Theorem 1 (Theorem 4 in [
43]).
Let be a family of topological metagroups, where ,
J is a set. Then, their direct product relative to the Tychonoff product topology is a topological metagroup, and Theorem 2 (Theorem 3 in [
41]).
Let the conditions of Remark 1 be fulfilled. Then, the Cartesian product supplied with a binary operation is a metagroup. Moreover, there are embeddings of A and B into ,
such that B is an almost normal submetagroup in .
If, in addition,
,
then B is a normal submetagroup. Theorem 3 (Theorem 4 in [
41]).
Suppose that the conditions of Remark 1 are satisfied. Then, the Cartesian product supplied with a binary operation is a metagroup. Moreover, there exist embeddings of A and B into ,
such that B is an almost normal submetagroup in .
If, additionally,
,
then B is a normal submetagroup. Definition 2 ([
41]).
We call the metagroup provided by Theorem 2 (or by Theorem 3) a smashed product (or a smashed twisted product, correspondingly) of metagroups A and B with smashing factors ϕ, η, κ and ξ. Lemma 1 (Lemma 5 in [
41], Lemma 1.1 in [
45]).
(a) Let D be a metagroup, and A be a submetagroup in D. Then, there exists a subset V in D such that D is a disjoint union of ,
where ;
that is,and .
If G is a left quasigroup, and H is a left subquasigroup in G, such that for each a and b in G, then there exists a transversal set for H in G.
Definition 3. A set V from Lemma 1 is called a transversal set of A in D.
Corollary 1 ([
41]).
Let D be a metagroup, A be a submetagroup in D, and V a transversal set of A in D. Then, Remark 2 (Remark 3 in [
41]).
We denote b in the decomposition by and ,
where τ and ψ is a shortened notation of and ,
respectively. That is, there are single-valued maps Remark 3 (Remark 4 in [
41]).
Let B and D be metagroups, A be a submetagroup in D, and V be a transversal of A in D. Also let Conditions –
be satisfied for A and B. We write(see also Remark 3 in [41] or 2 above). By Theorem 2, there exists a metagroup , where , for each .
It contains a submetagroupwhere is a support of ,
and denotes the cardinality of a set
.
Let for each and .
We writewhere J: ,
,
for each ,
and .
Then, for each ,
,
we writewhere for each ,
(see also and ).
Definition 4 ([
41]).
Suppose that the conditions of Remark 3 are satisfied, and on the Cartesian product (or ),
a binary operation is given by the following formula:
where for every d and in D, f and in F (or ,
respectively),
.
Theorem 4 (Theorem 5 in [
41]).
Let C,
,
D, F,
be the same as in Definition 4. Then, C and are loops, and there are natural embeddings ,
,
,
,
such that F (or )
is an almost normal subloop in C (or ,
respectively). Definition 5 ([
41]).
Product in loop C (or )
of Theorem 4 is called a smashed twisted wreath product of D and F (or a restricted smashed twisted wreath product of D and ,
respectively) with smashing factors ϕ, η, κ, ξ and it will be denoted by (or ,
respectively). The loop C (or )
is also called a smashed splitting extension of F (or of ,
respectively) by D.
Theorem 5 (Theorem 6 in [
41]).
Let the conditions of Remark 3 be satisfied, and ,
where is as in .
Then, C and supplied with the binary operation are metagroups. Theorem 6 (Theorem 2.1 in [
45]).
Assume that G is a topological quasigroup with a topology .
Assume also that H is a closed subquasigroup, such that ,
,
for each a and b in G. Then, for each x, b in G, the family is a local base for at ,
where is supplied with the quotient topology with respect to the quotient map .
Moreover, the map π is continuous and open, and is a homogeneous -
space. Theorem 7 (Theorem 2.3 in [
45]).
If the conditions of Theorem 6 are satisfied, then the quotient space is regular. Example 1. If the conditions of Corollary 1 in [41] or above are satisfied, either or ,
then the conditions ,
,
and for each a and b in G are satisfied for these pairs. Theorem 8 (Theorem 2.4 in [
45]).
Assume that G is a topological unital quasigroup, and H is a compact unital subquasigroup in G, satisfying the conditions of Theorem 6. Then, the quotient map is perfect. Corollary 2 (Corollary 2.4 in [
45]).
Suppose that the conditions of Theorem 8 are satisfied, and is compact. Then, G is compact. Corollary 3 (Corollary 2.5 in [
45]).
Assume that the conditions of Theorem 8 are satisfied, and the quotient space is compact. Let be a transversal set for H in G, and let V be supplied with a topology inherited from G. Then, V can be chosen compact and closed in G. Corollary 4 (Corollary 2.6 in [
45]).
If the conditions of Corollary 3 are satisfied, then the transversal set V and the transversal mapping can be chosen, such that and are continuous relative to topologies and on H and V, correspondingly, inherited from G. Corollary 5. Let the conditions of Corollary 1 in [41] or above be satisfied, and let and A and be closed in G; then, and are homogeneous spaces, and the quotient maps and are open. Proof. This follows from Theorems 2.1 and 2.3 in [
45], or Theorems 6 and 7 above, as their particular case.
The following corollaries, together with the assertions above, can serve for constructions of suitable examples. □
Corollary 6. Let the conditions of Remark 2 in [42] be satisfied, and let be compact and be as the topological quasigroup. Then, . Proof. Since
is the
topological quasigroup, then it is regular. In view of Corollary 3.1.14 in [
46],
. □
Corollary 7. Assume that the conditions of Remark 4 in [42] are satisfied, and is compact. Then, ; moreover, A and are compact relative to the topologies and , respectively, inherited from G. Proof. Corollary 6 implies that
. The maps
and
are continuous by the conditions of Remark 4 in [
42]. On the other hand,
and
; consequently,
A and
are closed in
D; hence,
A and
are compact by Theorem 3.1.2 in [
46]. □
Example 2. In particular, as pairs of A and B can be taken as the special orthogonal group of the Euclidean space , the special linear group of the Euclidean space is , where , A and B are supplied with topologies induced by the operator norm topology. Then, their central extensions can be taken, or semidirect products or smashed products with connected commutative groups. Then, using smashed products and smashed twisted wreath products, new metagroups are subsequently constructed using the theorems and corollaries above or given in the references.
Example 3. Let be the separable Hilbert space over the complex field , where is supplied with the standard multiplicative norm topology. We consider the unitary group and the general linear group of , where A and B are considered in the topologies inherited form the operator norm topology. Then, metagroups are constructed similarly to Example 2.
Other examples are 2–4 in [
43].
Possible applications and further developments are discussed in
Section 3.
2. Inverse Spectrum and Structure of Topological Metagroups
Theorem 9. Assume that the conditions of Remark 1 in [41] or above are satisfied, and is a smashed twisted product of metagroups A and B with smashing factors ϕ, η, κ, ξ. Then, embeddings and exist, and in G is invariant. Moreover, a transversal set exists such that . Proof. We shortly denote
as
, because
G is specified, and we write
with
for each
;
with
for each
. From Formula
in [
41] or
above, it follows that
for each
and
. Therefore, for each
in
G, there exist unique
and
, such that
since
by
in [
41] or
above. Certainly, the maps
and
provided by
are single-valued.
For each , , , we deduce that
and
by Conditions (31), (32), and (34) in [
41], or (4), (5), and (7) above. Hence,
with
; consequently,
satisfies
for each
a and
b in
G, since
by Remark 1 in [
41] or above.
In view of Lemma 1 and Formula
, the transversal set
and the maps
and
exist, such that
with
where
It remains to prove that
is invariant in
G. For this, it is sufficient to prove that
and
since Properties
and
imply that
for each
and
in
G.
For each in G and , we obtain
and
according to
in [
41] or
above. The following equation,
has a unique solution
for given
and
, since
satisfies Condition
in [
41] or
above. From
for each
and
in
G, and
, it follows that
. Thus,
G satisfies Condition
.
Then, we consider and for any and in G, and in B. Then, we infer that
and
by
and
in [
41], or
and
above. The following equation,
, is satisfied if and only if
, with
by
(i) and
(ii) in Definition 1. Using
,
and Lemma 2 in [
41], or
and
above, we deduce that there exists a unique solution,
with
, and
Since
and
,
, then
. From
and
in [
41], or
and
above, it follows that
Hence, and imply that ; consequently, G satisfies Condition . Thus, is the invariant submetagroup in G. □
Corollary 8. If the conditions of Remark 1 in [41] or above are satisfied, A and B are topological metagroups, the topology on G is induced by the Tychonoff product topology on , and the smashing factors ϕ, η, κ, ξ are (jointly) continuous, then the maps and are continuous relative to the topology on the topological metagroup . Proof. This follows from Formulas – and the (joint) continuity of the smashing factors , , , , and hence of and on , where the topology on G is induced by the Tychonoff product topology on . □
Corollary 9. For pairs of metagroups, let , (the conditions of Remark 1 in [41] or above) be satisfied for each , where , such that for each . Let for each and , and for each and . Let and , and let , , , for the pair with satisfy the conditions of Remark 1 in [41] or above (with instead of ), and let , where is the embedding provided by Theorem 9. Then, there are embeddings , for each , , such that D with and satisfy Condition in [41] or above, and for each . Proof. By virtue of Theorem 4 in [
41], or Theorem 3 above,
B,
and
D are metagroups and there are embeddings
,
for each
,
, such that
, since
.
For each , and with , , , we deduce that
and
Therefore,
if and only if
and
. From
and
in [
41], or
and
above, and the conditions of this corollary, it follows that
for each
, since
for each
and
. In view of Theorem 9, the subgroup
is invariant in
and
.
Certainly, and are isomorphic subgroups in D, since . Hence, each can be presented in the following form: with , and . From and , it follows that for each . On the other hand, , since for each . Consequently, the subgroup is invariant in D. □
Corollary 10. Assume that the conditions of Corollary 9 are satisfied, , are topological metagroups for each , and , , , are jointly continuous for each . Then, D, A, , provided by Corollaries 8 and 9, are topological metagroups and satisfy the conditions of Theorem 6 in [41] or Theorem 5 above, and is closed in D. Proof. This follows from Theorem 4 in [
41], or Theorem 3 above, and Corollaries 8 and 9 above. □
Definition 6. Let Λ be a directed set, be a topological metagroup (or quasigroup), and be a continuous homomorphism for each in Λ, such that for each in Λ, and for each , where for each . Then, is called an inverse spectrum of topological metagroups (or quasigroups, respectively). If a topological metagroup G is a limit of S, , then it is said that G is decomposed into S.
Theorem 10. There exists an infinite family , where each is a topological metagroup, such that G is compact, locally connected and can not be decomposed into the inverse spectrum of topological metagroups with for each .
Proof. We take any locally connected
compact metagroups
A,
B, and their invariant closed subgroup
with positive covering dimensions
,
,
,
, such that the conditions of Theorem 6 in [
41] or Theorem 5 above are satisfied. Evidently, such triples
exist, and their family is infinite. Indeed, in particular, they may be direct products
,
or semidirect products
,
with topological
metagroups
,
, and a topological
group
; or, in particular,
A,
B may be topological
groups (see also examples
–
in Remark 2 [
42]). □
Therefore,
is invariant in the smashed twisted product
, such that
G is a topological
metagroup, and a transversal set exists
by Corollary 1 in [
41] or above and Theorem 9. By virtue of Corollary 8, the maps
and
are continuous. For compact
A and
B, the metagroup
G is compact by the Tychonoff Theorem 3.2.4 in [
46].
This implies that there are triples
and
satisfying the conditions of Corollary 10 with locally connected
compact metagroups
,
,
, and their invariant closed subgroup
, with positive covering dimensions
,
,
,
,
,
. Then,
D,
A,
, provided by Corollaries 8 and 9, satisfy the conditions of Corollary 1 in [
41] or Theorem 9, such that
. By virtue of Theorem 6 in [
41] or Theorem 5 above, Theorem 1 in [
43], Theorem 2.4 in [
45], or Theorem 8 and Corollary 10 above,
D,
A,
B are locally connected
compact metagroups with a closed invariant subgroup
and
,
,
. Moreover,
, with
, and there is a bijection from
onto
by Remark 3 in [
42] and
by Formula
in [
42]. Therefore,
and
can be chosen to be compact; consequently,
is compact by the Tychonoff Theorem 3.2.4 in [
46]. Corollary 5 and Corollary 8 imply that the maps
and
are continuous relative to the topology
.
In view of Theorems 3 and 4 in [
42], there exists a
compact metagroup
, where
is closed in
, where
,
. Hence,
and
is locally connected. In view of Theorem 3.1.9 in [
46],
D,
A,
B,
,
are
topological spaces. By the construction above,
.
On the other hand, a family
of all continuous homomorphisms from
into
, satisfying
in [
41] or
above, is a proper closed subset in a family
of all continuous maps from
into
, satisfying
in [
41] or
above. Since
and
, then
, where
is in the
topology.
We choose with and the map with values in such that depends nontrivially on infinite number of coordinates for an infinite family of for each and , where d and belong to D, , , since and . This implies that there exists the topological metagroup with , which cannot be decomposed into the inverse spectrum of topological metagroups with for each . From the proof above, it follows that the family of such topological metagroups is infinite.
Remark 4. If, instead of Theorem 6, we use Theorem 5 in [41], or instead of Theorem 5, we use Theorem 4 above, then Theorem 10 will be for topological unital quasigroups (loops) G. Thus, Theorem 10 illustrates a principal structural distinction between topological groups and topological metagroups.