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Groups with some subgroups complemented Carmine Monetta University of Salerno Young Researchers Algebra Conference 2019 17th September 2019 Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019 This


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Groups with some subgroups complemented

Carmine Monetta University of Salerno Young Researchers Algebra Conference 2019 17th September 2019

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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This is a joint work1 with Sergio Camp-Mora, from Universitat Polit` ecnica de Val` encia.

  • S. Camp-Mora, C. Monetta,

Groups with some families of subgroups complemented, submitted.

1Funded by GNSAGA Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Complemented subgroups

A subgroup H of a group G is said to be complemented in G if there exist a subgroup K of G such that G = HK H ∩ K = 1 The subgroup K is called a complement of H in G. Example ⋆ The alternating group of degree n is always complemented in the symmetric group of degree n. ⋆ If G = x is the cyclic group of order 4, then the subgroup H = x2 is not complemented in G.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Some well-known facts

⋆ If K is a complement of H in G, then K detects a complete set of representative of both left and right cosets of H in G. ⋆ In a finite group every normal Hall subgroup has a complement, where H is a normal Hall subgroup of a group G if (|H|, |G/H|) = 1. ⋆ The concept of complement generalizes that of direct and semidirect factor.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Some well-known facts

⋆ If K is a complement of H in G, then K detects a complete set of representative of both left and right cosets of H in G. ⋆ In a finite group every normal Hall subgroup has a complement, where H is a normal Hall subgroup of a group G if (|H|, |G/H|) = 1. ⋆ The concept of complement generalizes that of direct and semidirect factor.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Some well-known facts

⋆ If K is a complement of H in G, then K detects a complete set of representative of both left and right cosets of H in G. ⋆ In a finite group every normal Hall subgroup has a complement, where H is a normal Hall subgroup of a group G if (|H|, |G/H|) = 1. ⋆ The concept of complement generalizes that of direct and semidirect factor.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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C-groups

A group G is said to be a C-group if all its subgroups are complemented. Remark The class of all C-groups is closed with respect to forming subgroups, images and direct products. Let H be a subgroup of a C-group G. Then, every subgroup L of H admits a complement K in G, that is G = LK L ∩ K = 1 Then K1 = K ∩ H is a complement of L in H because LK1 = L(K ∩ H) = LK ∩ H = G ∩ H = H L ∩ K1 = L ∩ (K ∩ H) = 1

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A characterization of finite C-groups

Recall that a group G has the subgroup lattice complemented if for every H ≤ G there exists K ≤ G such that G = H, K H ∩ K = 1 Theorem (P. Hall) For a finite group G, the following condition are equivalent.

1 G is a C-group. 2 G is a supersoluble and the subgroup lattice of G is complemented. 3 G is isomorphic to a subgroup of a direct product of groups of

squarefree orders.

  • P. Hall,

Complemented groups, Journal of London Mathematical Society, 12 (1937), 201-204.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A characterization of finite C-groups

Recall that a group G has the subgroup lattice complemented if for every H ≤ G there exists K ≤ G such that G = H, K H ∩ K = 1 Theorem (P. Hall) For a finite group G, the following condition are equivalent.

1 G is a C-group. 2 G is a supersoluble and the subgroup lattice of G is complemented. 3 G is isomorphic to a subgroup of a direct product of groups of

squarefree orders.

  • P. Hall,

Complemented groups, Journal of London Mathematical Society, 12 (1937), 201-204.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A characterization of finite C-groups

Recall that a group G has the subgroup lattice complemented if for every H ≤ G there exists K ≤ G such that G = H, K H ∩ K = 1 Theorem (P. Hall) For a finite group G, the following condition are equivalent.

1 G is a C-group. 2 G is a supersoluble and the subgroup lattice of G is complemented. 3 G is isomorphic to a subgroup of a direct product of groups of

squarefree orders.

  • P. Hall,

Complemented groups, Journal of London Mathematical Society, 12 (1937), 201-204.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A characterization of finite C-groups

Recall that a group G has the subgroup lattice complemented if for every H ≤ G there exists K ≤ G such that G = H, K H ∩ K = 1 Theorem (P. Hall) For a finite group G, the following condition are equivalent.

1 G is a C-group. 2 G is a supersoluble and the subgroup lattice of G is complemented. 3 G is isomorphic to a subgroup of a direct product of groups of

squarefree orders.

  • P. Hall,

Complemented groups, Journal of London Mathematical Society, 12 (1937), 201-204.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 23

A characterization of finite C-groups

Recall that a group G has the subgroup lattice complemented if for every H ≤ G there exists K ≤ G such that G = H, K H ∩ K = 1 Theorem (P. Hall) For a finite group G, the following condition are equivalent.

1 G is a C-group. 2 G is a supersoluble and the subgroup lattice of G is complemented. 3 G is isomorphic to a subgroup of a direct product of groups of

squarefree orders.

  • P. Hall,

Complemented groups, Journal of London Mathematical Society, 12 (1937), 201-204.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 27

Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-29
SLIDE 29

Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-30
SLIDE 30

Characterization of C-groups

Recall that a group G is hypercyclic if there exists an ascending normal series 1 ≤ H1 ≤ H2 ≤ · · · such that Hi is a normal subgroup of G and Hi+1/Hi is cyclic for every i ≥ 1. Theorem (N. V. Cernikova) For a group G, the following condition are equivalent.

1 G is a C-group. 2 G is a hypercyclic and the subgroup lattice of G is complemented. 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and Ai normal in G for all i ∈ I.

  • N. V. Chernikova,

Groups with complemented subgroups, American Mathematical Society Translations, 17 (1961), 153-172.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Question

What about a group if only some of its subgroups are complemented?

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Sylow subgroups complemented

Theorem (P. Hall) A finite group G is soluble if and only if every Sylow subgroup of G is complemented.

  • P. Hall,

Complemented groups, J. of London Math. Soc., 12 (1937), 201-204.

Theorem (Z. Arad, M. B. Ward) A finite group G is soluble if and only if all Sylow 2-subgroups and all Sylow 3-subgroups are complemented.

  • Z. Arad, M. B. Ward,

New criteria for the solvability of finite groups, J. Algebra 77 (1982), 234-246.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 33

Sylow subgroups complemented

Theorem (P. Hall) A finite group G is soluble if and only if every Sylow subgroup of G is complemented.

  • P. Hall,

Complemented groups, J. of London Math. Soc., 12 (1937), 201-204.

Theorem (Z. Arad, M. B. Ward) A finite group G is soluble if and only if all Sylow 2-subgroups and all Sylow 3-subgroups are complemented.

  • Z. Arad, M. B. Ward,

New criteria for the solvability of finite groups, J. Algebra 77 (1982), 234-246.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 34

Sylow subgroups complemented

Theorem (P. Hall) A finite group G is soluble if and only if every Sylow subgroup of G is complemented.

  • P. Hall,

Complemented groups, J. of London Math. Soc., 12 (1937), 201-204.

Theorem (Z. Arad, M. B. Ward) A finite group G is soluble if and only if all Sylow 2-subgroups and all Sylow 3-subgroups are complemented.

  • Z. Arad, M. B. Ward,

New criteria for the solvability of finite groups, J. Algebra 77 (1982), 234-246.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 35

Sylow subgroups complemented

Theorem (P. Hall) A finite group G is soluble if and only if every Sylow subgroup of G is complemented.

  • P. Hall,

Complemented groups, J. of London Math. Soc., 12 (1937), 201-204.

Theorem (Z. Arad, M. B. Ward) A finite group G is soluble if and only if all Sylow 2-subgroups and all Sylow 3-subgroups are complemented.

  • Z. Arad, M. B. Ward,

New criteria for the solvability of finite groups, J. Algebra 77 (1982), 234-246.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-36
SLIDE 36

Sylow subgroups complemented

Theorem (P. Hall) A finite group G is soluble if and only if every Sylow subgroup of G is complemented.

  • P. Hall,

Complemented groups, J. of London Math. Soc., 12 (1937), 201-204.

Theorem (Z. Arad, M. B. Ward) A finite group G is soluble if and only if all Sylow 2-subgroups and all Sylow 3-subgroups are complemented.

  • Z. Arad, M. B. Ward,

New criteria for the solvability of finite groups, J. Algebra 77 (1982), 234-246.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 37

A new characterization of finite C-groups

  • A. Ballester-Bolinches and Guo Xiuyun analyzed the class of groups in

which every minimal subgroup is complemented, where a minimal subgroup is a subgroup of prime order. Theorem (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is supersoluble with elementary abelian Sylow subgroups

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 38

A new characterization of finite C-groups

  • A. Ballester-Bolinches and Guo Xiuyun analyzed the class of groups in

which every minimal subgroup is complemented, where a minimal subgroup is a subgroup of prime order. Theorem (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is supersoluble with elementary abelian Sylow subgroups

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 39

A new characterization of finite C-groups

  • A. Ballester-Bolinches and Guo Xiuyun analyzed the class of groups in

which every minimal subgroup is complemented, where a minimal subgroup is a subgroup of prime order. Theorem (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is supersoluble with elementary abelian Sylow subgroups

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 40

A new characterization of finite C-groups

  • A. Ballester-Bolinches and Guo Xiuyun analyzed the class of groups in

which every minimal subgroup is complemented, where a minimal subgroup is a subgroup of prime order. Theorem (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is supersoluble with elementary abelian Sylow subgroups

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A new characterization of finite C-groups

Corollary (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is a C-group.

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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A new characterization of finite C-groups

Corollary (A. Ballester-Bolinches, Guo Xiuyun) A finite group G has all minimal subgroups complemented if and only if G is a C-group.

  • A. Ballester-Bolinches, Guo Xiuyun,

On complemented subgroups of finite groups, Archiv der Mathematik, 72 (1999), 161-166.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Infinite version

Theorem (Yu. M. Gorchakov) Let G be a periodic group. Then G has every minimal subgroup complemented if and only if G is isomorphic to a subgroup of the cartesian product Crn≥1 Hn, where Hn are completely primitive groups.

  • Yu. M. Gorchakov,

On primarily factorizable groups, Ukrainian Mathematical Journal, 14 (1962), 3-9.

If p is a prime, and P is a group of order p, a completely primitive group is a subgroup of P ⋊ Aut P.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 44

Infinite version

Theorem (Yu. M. Gorchakov) Let G be a periodic group. Then G has every minimal subgroup complemented if and only if G is isomorphic to a subgroup of the cartesian product Crn≥1 Hn, where Hn are completely primitive groups.

  • Yu. M. Gorchakov,

On primarily factorizable groups, Ukrainian Mathematical Journal, 14 (1962), 3-9.

If p is a prime, and P is a group of order p, a completely primitive group is a subgroup of P ⋊ Aut P.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-45
SLIDE 45

Infinite version

Theorem (Yu. M. Gorchakov) Let G be a periodic group. Then G has every minimal subgroup complemented if and only if G is isomorphic to a subgroup of the cartesian product Crn≥1 Hn, where Hn are completely primitive groups.

  • Yu. M. Gorchakov,

On primarily factorizable groups, Ukrainian Mathematical Journal, 14 (1962), 3-9.

If p is a prime, and P is a group of order p, a completely primitive group is a subgroup of P ⋊ Aut P.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-46
SLIDE 46

Infinite version

Theorem (Yu. M. Gorchakov) Let G be a periodic group. Then G has every minimal subgroup complemented if and only if G is isomorphic to a subgroup of the cartesian product Crn≥1 Hn, where Hn are completely primitive groups.

  • Yu. M. Gorchakov,

On primarily factorizable groups, Ukrainian Mathematical Journal, 14 (1962), 3-9.

If p is a prime, and P is a group of order p, a completely primitive group is a subgroup of P ⋊ Aut P.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-47
SLIDE 47

Infinite version

Theorem (Yu. M. Gorchakov) Let G be a periodic group. Then G has every minimal subgroup complemented if and only if G is isomorphic to a subgroup of the cartesian product Crn≥1 Hn, where Hn are completely primitive groups.

  • Yu. M. Gorchakov,

On primarily factorizable groups, Ukrainian Mathematical Journal, 14 (1962), 3-9.

If p is a prime, and P is a group of order p, a completely primitive group is a subgroup of P ⋊ Aut P.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 48

Our context

We considered a narrower setting, taking into account only Locally Soluble groups, that is, groups whose finitely generated subgroups are soluble. The first family of subgroups we considered is that of

Cyclic subgroups

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-49
SLIDE 49

Our context

We considered a narrower setting, taking into account only Locally Soluble groups, that is, groups whose finitely generated subgroups are soluble. The first family of subgroups we considered is that of

Cyclic subgroups

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

slide-50
SLIDE 50

Our context

We considered a narrower setting, taking into account only Locally Soluble groups, that is, groups whose finitely generated subgroups are soluble. The first family of subgroups we considered is that of

Cyclic subgroups

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 52

Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 53

Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 56

Cyclic subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a locally soluble group. Then the following properties are equivalent.

1 Every cyclic subgroup of G is complemented 2 G is periodic and every minimal subgroup of G is complemented 3 G is the semidirect product of A = Dri∈I Ai by B = Drj∈J Bj where

all the Ai and Bj have prime order, and A has a set of maximal subgroups normal in G with trivial intersection.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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SLIDE 57

Question

A group whose cyclic subgroups are complemented, is necessarily a C-group? In general, the answer is NO!

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Question

A group whose cyclic subgroups are complemented, is necessarily a C-group? In general, the answer is NO!

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Negative Answer

Counter-example (S. Camp-Mora, C. M.) Let H = Dri≥1xi and B = Drj≥1yj where xi has order 3 and yj has

  • rder 2 for every i, j ≥ 1.

We define the following action: xi yn =    xi+2n−1 if i ≡ 1, . . . , 2n−1 mod 2n xi−2n−1 if i ≡ 2n−1 + 1, . . . , 2n mod 2n for every i, n ≥ 1. Then, G = H, B = HB has every minimal subgroup complemented, but G does not contain any normal minimal subgroup, that is, G is not a C-group.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Negative Answer

Counter-example (S. Camp-Mora, C. M.) Let H = Dri≥1xi and B = Drj≥1yj where xi has order 3 and yj has

  • rder 2 for every i, j ≥ 1.

We define the following action: xi yn =    xi+2n−1 if i ≡ 1, . . . , 2n−1 mod 2n xi−2n−1 if i ≡ 2n−1 + 1, . . . , 2n mod 2n for every i, n ≥ 1. Then, G = H, B = HB has every minimal subgroup complemented, but G does not contain any normal minimal subgroup, that is, G is not a C-group.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Negative Answer

Counter-example (S. Camp-Mora, C. M.) Let H = Dri≥1xi and B = Drj≥1yj where xi has order 3 and yj has

  • rder 2 for every i, j ≥ 1.

We define the following action: xi yn =    xi+2n−1 if i ≡ 1, . . . , 2n−1 mod 2n xi−2n−1 if i ≡ 2n−1 + 1, . . . , 2n mod 2n for every i, n ≥ 1. Then, G = H, B = HB has every minimal subgroup complemented, but G does not contain any normal minimal subgroup, that is, G is not a C-group.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Negative Answer

Counter-example (S. Camp-Mora, C. M.) Let H = Dri≥1xi and B = Drj≥1yj where xi has order 3 and yj has

  • rder 2 for every i, j ≥ 1.

We define the following action: xi yn =    xi+2n−1 if i ≡ 1, . . . , 2n−1 mod 2n xi−2n−1 if i ≡ 2n−1 + 1, . . . , 2n mod 2n for every i, n ≥ 1. Then, G = H, B = HB has every minimal subgroup complemented, but G does not contain any normal minimal subgroup, that is, G is not a C-group.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Families of subgroups

The second family of subgroups we considered is that of

Infinite rank subgroups

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Families of subgroups

The second family of subgroups we considered is that of

Infinite rank subgroups

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Pr¨ ufer rank

A group G is said to have finite (Pr¨ ufer) rank r if every finitely generated subgroup of G can be generated by at most r elements r is the least positive integer with such property If there is no such an r, the group G has infinite rank. Example ⋆ Cp∞, Q are locally cyclic groups, so they have rank 1 ⋆ Every polycyclic group has finite rank ⋆ Any free non-abelian group has infinite rank

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Why locally soluble groups?

Theorem (A. I. Mal’cev) A locally nilpotent group of infinite rank must contain an abelian subgroup

  • f infinite rank.
  • A. I. Mal’cev,

On certain classes of infinite soluble groups, Amer. Math. Soc. Translation 2 (1956), 1-21.

Theorem (V. P. ˘ Sunkov) A locally finite group with all abelian subgroups of finite rank itself has finite rank.

  • V. P. ˘

Sunkov, On locally finite groups of finite rank, Algebra and Logic 10 (1971), 127-142.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Why locally soluble groups?

Theorem (A. I. Mal’cev) A locally nilpotent group of infinite rank must contain an abelian subgroup

  • f infinite rank.
  • A. I. Mal’cev,

On certain classes of infinite soluble groups, Amer. Math. Soc. Translation 2 (1956), 1-21.

Theorem (V. P. ˘ Sunkov) A locally finite group with all abelian subgroups of finite rank itself has finite rank.

  • V. P. ˘

Sunkov, On locally finite groups of finite rank, Algebra and Logic 10 (1971), 127-142.

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Why locally soluble groups?

Theorem (Y. I. Merzljakov) There exist locally soluble groups of infinite rank in which every abelian subgroup has finite rank.

  • Y. I. Merzljakov,

Locally soluble groups of finite rank, Algebra and Logic 8 (1969), 686-690.

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Strong influence

Theorem (M. R. Dixon, M. J. Evans, H. Smith) Let c be a positive integer and let G be a locally soluble group of infinite rank whose proper subgroups of infinite rank are nilpotent with class at most c. Then G is nilpotent of class at most c.

  • M. R. Dixon, M. J. Evans, H. Smith,

Locally (soluble-by-finite) groups with all proper insoluble subgroups of finite rank, Arch. Math. (Basel) 68 (1997), 100-109.

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Strong influence

Theorem (M. R. Dixon, M. J. Evans, H. Smith) Let k be a positive integer and let G be a soluble group of infinite rank whose proper subgroups of infinite rank have derived length at most k. Then G has derived length at most k.

  • M. R. Dixon, M. J. Evans, H. Smith,

Locally (soluble-by-finite) groups with all proper non-nilpotent subgroups of finite rank, J. Pure Appl. Algebra 135 (1999), 33-43.

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Strong influence

Theorem (M. De Falco, F. de Giovanni, C. Musella, N. Trabelsi) Let G be a locally soluble group of infinite rank. If all proper subgroups of infinite rank of G have locally finite commutator subgroup, then G ′ is locally finite.

  • M. De Falco, F. de Giovanni, C. Musella, N. Trabelsi,

Groups with restrictions on subgroups of infinite rank, Rev. Mat. Iberoamericana 2 (2014).

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Infinite rank subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a periodic locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, then G is a C-group. Open Problem Let G be a locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, is then G a C-group?

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Infinite rank subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a periodic locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, then G is a C-group. Open Problem Let G be a locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, is then G a C-group?

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Infinite rank subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a periodic locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, then G is a C-group. Open Problem Let G be a locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, is then G a C-group?

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019

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Infinite rank subgroups Complemented

Theorem (S. Camp-Mora, C. M.) Let G be a periodic locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, then G is a C-group. Open Problem Let G be a locally soluble group of infinite rank. If every infinite rank subgroup of G is complemented in G, is then G a C-group?

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Thank you for the attention!

Groups with some subgroups complemented Carmine MONETTA Young Researchers Algebra Conference 2019