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<Chapter Label="ESSP">

<Heading>Shoda pairs</Heading>

<Section Label="ESSPESSP">
<Heading>Computing extremely strong Shoda pairs</Heading>

<ManSection>
   <Attr Name="ExtremelyStrongShodaPairs"
         Arg="G"
         Comm="A list of ESSPs representatives realizing Wedderburn components of QG" />
   <Returns>
         A list of pairs of subgroups of the input group.
   </Returns>
   <Description>
        The input should be a finite group <A>G</A>.
        <P/>
        Computes a list of representatives of the equivalence classes of
        <E>extremely strong Shoda pairs</E>
        (<Ref Sect="ESSPDef" />) of a finite group <A>G</A>.
        <P/>

<Example>
<![CDATA[
gap> ExtremelyStrongShodaPairs(DihedralGroup(32));
[ [ <pc group of size 32 with 5 generators>,
      <pc group of size 32 with 5 generators> ],
  [ <pc group of size 32 with 5 generators>,
      Group([ f1*f2*f3*f4*f5, f3, f4, f5 ]) ],
  [ <pc group of size 32 with 5 generators>, Group([ f2, f3, f4, f5 ]) ],
  [ <pc group of size 32 with 5 generators>, Group([ f1, f3, f4, f5 ]) ],
  [ Group([ f1*f2*f3*f4*f5, f3, f4, f5 ]), Group([ f1*f2*f4*f5, f4, f5 ]) ],
  [ Group([ f2, f3, f4, f5 ]), Group([ f5 ]) ],
  [ Group([ f2, f3, f4, f5 ]), Group([  ]) ] ]
gap> ExtremelyStrongShodaPairs(SL(2,3));
[ [ SL(2,3), SL(2,3) ],
  [ SL(2,3),
      Group([ [ [ Z(3)^0, Z(3)^0 ], [ Z(3)^0, Z(3) ] ],
          [ [ Z(3), Z(3)^0 ], [ Z(3)^0, Z(3)^0 ] ],
          [ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]) ],
  [
      Group([ [ [ Z(3)^0, Z(3)^0 ], [ Z(3)^0, Z(3) ] ],
          [ [ Z(3), Z(3)^0 ], [ Z(3)^0, Z(3)^0 ] ],
          [ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]),
      Group([ [ [ 0*Z(3), Z(3) ], [ Z(3)^0, 0*Z(3) ] ],
          [ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]) ] ]
gap> ExtremelyStrongShodaPairs(SymmetricGroup(5));
[ [ Sym( [ 1 .. 5 ] ), Sym( [ 1 .. 5 ] ) ],
  [ Sym( [ 1 .. 5 ] ), Alt( [ 1 .. 5 ] ) ] ]
]]>
</Example>

   </Description>
</ManSection>

</Section>

<Heading>Strong Shoda pairs</Heading>

<Section Label="SSPSSP">
<Heading>Computing strong Shoda pairs</Heading>

<ManSection>
   <Attr Name="StrongShodaPairs"
         Arg="G"
         Comm="A list of SSPs representatives realizing Wedderburn components of QG" />
   <Returns>
         A list of pairs of subgroups of the input group.
   </Returns>
   <Description>
        The input should be a finite group <A>G</A>.
        <P/>
        Computes a list of representatives of the equivalence classes of
        <E>strong Shoda pairs</E>
        (<Ref Sect="SSPDef" />) of a finite group <A>G</A>.
        <P/>

<Example>
<![CDATA[
gap> ssp:=StrongShodaPairs( SymmetricGroup(4) );;
gap> Length(ssp);
5
gap> List(ssp,x->List(x,StructureDescription));
[ [ "S4", "S4" ], [ "S4", "A4" ], [ "A4", "C2 x C2" ], [ "D8", "C2 x C2" ],
  [ "D8", "C4" ] ]
gap> ssp:=StrongShodaPairs( DihedralGroup(64) );;
gap> Length(ssp);
8
gap> List(ssp,x->List(x,StructureDescription));
[ [ "D64", "D64" ], [ "D64", "D32" ], [ "D64", "C32" ], [ "D64", "D32" ],
  [ "D32", "D16" ], [ "C32", "C4" ], [ "C32", "C2" ], [ "C32", "1" ] ]
]]>
</Example>

   </Description>
</ManSection>

</Section>

<Section Label="IsSSP">
<Heading>Properties related with Shoda pairs</Heading>

<ManSection>
   <Oper Name="IsExtremelyStrongShodaPair"
         Arg="G K H"
         Comm="Is (K,H) an extremely strong Shoda pair of G?" />
   <Description>
         The first argument should be a finite group <A>G</A>,
         the second one a normal sugroup <A>K</A> of <A>G</A> and the
         third one a subgroup of <A>K</A>. <P/>

         Returns <K>true</K> if (<A>K</A>,<A>H</A>) is an
         <E>extremely strong Shoda pair</E> (<Ref Sect="ESSPDef" />)
         of <A>G</A>, and <K>false</K> otherwise.

<Example>
<![CDATA[
gap> G:=SymmetricGroup(4);; K:=Group( (1,3,2,4), (3,4) );;
gap> H1:=Group( (2,4,3), (1,4)(2,3), (1,3)(2,4) );;
gap> H2:=Group( (3,4), (1,2)(3,4) );;
gap> IsExtremelyStrongShodaPair( G, G, H1 );
true
gap> IsExtremelyStrongShodaPair( G, K, H2 );
false
gap> IsExtremelyStrongShodaPair( G, G, H2 );
false
gap> IsExtremelyStrongShodaPair( G, G, K );
false
]]>
</Example>

   </Description>
</ManSection>

<ManSection>
   <Oper Name="IsStrongShodaPair"
         Arg="G K H"
         Comm="Is (K,H) a strong Shoda pair of G?" />
   <Description>
         The first argument should be a finite group <A>G</A>,
         the second one a sugroup <A>K</A> of <A>G</A> and the
         third one a subgroup of <A>K</A>. <P/>

         Returns <K>true</K> if (<A>K</A>,<A>H</A>) is a
         <E>strong Shoda pair</E> (<Ref Sect="SSPDef" />)
         of <A>G</A>, and <K>false</K> otherwise. <P/>

         Note that every extremely strong Shoda pair is a strong Shoda pair,
         but the converse is not true.

<Example>
<![CDATA[
gap> G:=SymmetricGroup(4);; K:=Group( (1,3,2,4), (3,4) );;
gap> H1:=Group( (2,4,3), (1,4)(2,3), (1,3)(2,4) );;
gap> H2:=Group( (3,4), (1,2)(3,4) );;
gap> IsStrongShodaPair( G, G, H1 );
true
gap> IsExtremelyStrongShodaPair( G, K, H2 );
false
gap> IsStrongShodaPair( G, K, H2 );
true
gap> IsStrongShodaPair( G, G, K );
false
]]>
</Example>

   </Description>
</ManSection>

<ManSection>
   <Oper Name="IsShodaPair"
         Arg="G K H"
         Comm="Is (K,H) a Shoda pair of G?" />
   <Description>
         The first argument should be a finite group <A>G</A>,
         the second a subgroup <A>K</A> of <A>G</A> and the
         third one a subgroup of <A>K</A>. <P/>

         Returns <K>true</K> if (<A>K</A>,<A>H</A>) is a
         <E>Shoda pair</E> (<Ref Sect="SPDef" />) of <A>G</A>.<P/>

         Note that every strong Shoda pair is a Shoda pair,
         but the converse is not true.

<Example>
<![CDATA[
gap> G:=AlternatingGroup(5);;
gap> K:=AlternatingGroup(4);;
gap> H := Group( (1,2)(3,4), (1,3)(2,4) );;
gap> IsStrongShodaPair( G, K, H );
false
gap> IsShodaPair( G, K, H );
true
]]>
</Example>

   </Description>
</ManSection>
<Alt Only="LaTeX">\newpage</Alt>
<ManSection>
   <Oper Name="IsStronglyMonomial"
         Arg="G"
         Comm="Is every irreducible character strongly monomial" />
   <Description>
        The input <A>G</A> should be a finite group. <P/>

        Returns <K>true</K> if <A>G</A> is a <E>strongly monomial</E>
        (<Ref Sect="StMon" />) finite group.

<Example>
<![CDATA[
gap> S4:=SymmetricGroup(4);;
gap> IsStronglyMonomial(S4);
true
gap> G:=SmallGroup(24,3);;
gap> IsStronglyMonomial(G);
false
gap> IsMonomial(G);
false
gap> G:=SmallGroup(1000,86);;
gap> IsMonomial(G);
true
gap> IsStronglyMonomial(G);
false
]]>
</Example>

   </Description>
</ManSection>

<ManSection>
   <Oper Name="IsNormallyMonomial"
         Arg="G"
         Comm="Is every irreducible character normally monomial" />
   <Description>
        The input <A>G</A> should be a finite group. <P/>

        Returns <K>true</K> if <A>G</A> is a finite <E>normally monomial</E>
        (<Ref Sect="NorMon" />) group.

<Example>
<![CDATA[
gap>  D24:=DihedralGroup(24);
<pc group of size 24 with 4 generators>
gap> IsNormallyMonomial(D24);
true
gap> G:=SmallGroup(192,1023);
<pc group of size 192 with 7 generators>
gap> IsNormallyMonomial(G);
true
gap> G:=SmallGroup(1029,12);
<pc group of size 1029 with 4 generators>
gap> IsNormallyMonomial(G);
false
gap> IsStronglyMonomial(G);
true
gap> G:=SL(2,3);
SL(2,3)
gap> IsNormallyMonomial(G);
false
gap> IsStronglyMonomial(G);
false
]]>
</Example>

   </Description>
</ManSection>

</Section>

</Chapter>

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