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loops/gap/quasigroups.gi
Glen Whitney 87e7b01333 provide facility to bind element names
2017-10-19 02:08:47 +02:00

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#############################################################################
##
#W quasigroups.gi Representing, creating and displaying quasigroups [loops]
##
#H @(#)$Id: creation.gi, v 3.2.0 2015/11/22 gap Exp $
##
#Y Copyright (C) 2004, G. P. Nagy (University of Szeged, Hungary),
#Y P. Vojtechovsky (University of Denver, USA)
##
#############################################################################
## TESTING MULTIPLICATION TABLES
## -------------------------------------------------------------------------
#############################################################################
##
#O IsLeftQuasigroupTable( ls )
##
## Returns true if <ls> is an n by n matrix with n distinct
## integral entries, each occurring exactly once in each row
InstallMethod( IsLeftQuasigroupTable, "for matrix",
[ IsMatrix ],
function( ls )
local first_row;
# checking rows
first_row := Set( ls[ 1 ] );
if not Length( first_row ) = Length( ls[ 1 ] ) then return false; fi;
if ForAll( ls, row -> Set( row ) = first_row ) = false then return false; fi;
return true;
end );
#############################################################################
##
#O IsRightQuasigroupTable( ls )
##
## Returns true if <ls> is an n by n matrix with n distinct
## integral entries, each occurring exactly once in each column
InstallMethod( IsRightQuasigroupTable, "for matrix",
[ IsMatrix ],
mat -> IsLeftQuasigroupTable(TransposedMat(mat))
);
#############################################################################
##
#O IsLoopTable( ls )
##
## Returns true if <ls> is a normalized latin square. An n by n latin square
## is normalized if the first row and first column read the same, and the
## entries in the first row are ordered.
InstallMethod( IsLoopTable, "for matrix",
[ IsMatrix ],
function( ls )
if not IsQuasigroupTable( ls ) then return false; fi;
return Set( ls[ 1 ] ) = ls[ 1 ]
and ls[ 1 ] = List( [1..Length(ls)], i -> ls[ i ][ 1 ] );
end );
#############################################################################
##
#O CanonicalCayleyTableOfLeftQuasigroupTable( ls )
##
## Returns a Cayley table isomorphic to <ls>, which must already be known
## to be a left quasigroup table, in which the entries of ls
## have been replaced by numerical values 1, ..., n in the following way:
## Let e_1 < ... < e_n be all distinct entries of ls. Then e_i is renamed
## to i. In particular, when {e_1,...e_n} = {1,...,n}, the operation
## does nothing.
InstallGlobalFunction( CanonicalCayleyTableOfLeftQuasigroupTable,
function( ls )
local n, entries, i, j, T;
n := Length( ls );
# finding all distinct entries in the table
entries := [];
for i in ls[1] do
AddSet( entries, i );
od;
if entries = [1..n] then return List(ls, l -> ShallowCopy(l));
fi;
# renaming the entries and making a mutable copy, too
T := List( [1..n], i -> [1..n] );
for i in [1..n] do for j in [1..n] do
T[ i ][ j ] := Position( entries, ls[ i ][ j ] );
od; od;
return T;
end );
#############################################################################
##
#O CanonicalCayleyTable( ls )
##
## Returns a Cayley table isomorphic to <ls>, in which the entries of ls
## have been replaced by numerical values 1, ..., n in the following way:
## Let e_1 < ... < e_n be all distinct entries of ls. Then e_i is renamed
## to i. In particular, when {e_1,...e_n} = {1,...,n}, the operation
## does nothing.
InstallMethod( CanonicalCayleyTable, "for matrix",
[ IsMatrix ],
function( ls )
local n, entries, i, j, T;
n := Length( ls );
# finding all distinct entries in the table
entries := [];
for i in [1..n] do for j in [1..n] do
AddSet( entries, ls[ i ][ j ] );
od; od;
if entries = [1..n] then return List(ls, l -> ShallowCopy(l));
fi;
# renaming the entries and making a mutable copy, too
T := List( [1..n], i -> [1..n] );
for i in [1..n] do for j in [1..n] do
T[ i ][ j ] := Position( entries, ls[ i ][ j ] );
od; od;
return T;
end);
#############################################################################
##
#O NormalizedQuasigroupTable( ls )
##
## Given a latin square <ls>, returns the corresponding normalized
## latin square with entries 1, ..., n.
InstallMethod( NormalizedQuasigroupTable, "for matrix",
[ IsMatrix ],
function( ls )
local T, perm;
if not IsQuasigroupTable( ls ) then
Error( "LOOPS: <1> must be a latin square." );
fi;
# renaming the entries to be 1, ..., n
T := CanonicalCayleyTableOfLeftQuasigroupTable( ls );
# permuting the columns so that the first row reads 1, ..., n
perm := PermList( T[ 1 ] );
T := List( T, row -> Permuted( row, perm ) );
# permuting the rows so that the first column reads 1, ..., n
return Set( T );
end );
#############################################################################
## CREATING QUASIGROUPS AND LOOPS MANUALLY
## -------------------------------------------------------------------------
#############################################################################
##
#A CayleyTable( Q )
##
## Returns the Cayley table of the magma <Q>. This is just like
## its multiplication table, except in case Q is a submagma of P, in which
## case the entries used are the indices in P rather than in Q.
InstallMethod( CayleyTable, "for magma",
[ IsMagma ],
function( Q )
local elms, parent_elms;
elms := Elements( Q );
parent_elms := Elements( Parent( Q ) );
return List( elms, x-> List( elms, y -> Position( parent_elms, x * y ) ) );
end );
#############################################################################
##
#O QuasigroupByCayleyTable( ct )
##
## Returns quasigroup with multiplication table <ct>.
InstallMethod( QuasigroupByCayleyTable, "for matrix",
[ IsMatrix ],
function( ct )
local F, Q, elms, n;
if not IsQuasigroupTable( ct ) then
Error( "LOOPS: <1> must be a latin square." );
fi;
# Making sure that entries are 1, ..., n
ct := CanonicalCayleyTableOfLeftQuasigroupTable( ct );
# constructing the family
F := NewFamily( "QuasigroupByCayleyTableFam", IsQuasigroupElement );
# installing data for the family
n := Length ( ct );
F!.size := n;
elms := Immutable( List( [1..n], i -> Objectify(
NewType( F, IsQuasigroupElement and IsQuasigroupElmRep), [ i ] ) ) );
F!.set := elms;
F!.cayleyTable := ct;
F!.elmNamePrefix := "q";
# creating the quasigroup
Q := Objectify( NewType( FamilyObj( elms ),
IsQuasigroup and IsAttributeStoringRep ), rec() );
# setting attributes for the quasigroup
SetSize( Q, n );
SetAsSSortedList( Q, elms );
SetParent( Q, Q );
SetCayleyTable( Q, ct );
SetConstructorFromTable(Q, QuasigroupByCayleyTable);
return Q;
end );
#############################################################################
##
#O LoopByCayleyTable( ct )
##
## Returns loop with multiplication table <ct>.
InstallMethod( LoopByCayleyTable, "for matrix",
[ IsMatrix ],
function( ct )
local F, L, elms, n;
if not IsLoopTable( ct ) then
Error( "LOOPS: <1> must be a normalized latin square." );
fi;
# Making sure that the entries are 1, ..., n.
# The table will remain normalized.
ct := CanonicalCayleyTableOfLeftQuasigroupTable( ct );
# constructing the family
F := NewFamily( "LoopByCayleyTableFam", IsLoopElement );
# installing the data for the family
n := Length ( ct );
F!.size := n;
elms := Immutable( List( [1..n], i -> Objectify(
NewType( F, IsLoopElement and IsLoopElmRep), [ i ] ) ) );
F!.set := elms;
F!.cayleyTable := ct;
F!.elmNamePrefix := "l";
# creating the loop
L := Objectify( NewType( FamilyObj( elms ),
IsLoop and IsAttributeStoringRep ), rec() );
# setting attributes for the loop
SetSize( L, n );
SetAsSSortedList( L, elms );
SetParent( L, L );
SetCayleyTable( L, ct );
SetOne( L, elms[ 1 ] );
SetConstructorFromTable(L, LoopByCayleyTable);
return L;
end );
#############################################################################
##
#O SpecifyElmNamePrefix( C, name )
##
## Sets the elmNamePrefix property on the family of a Represntative of
## collection <C>. For quasigroups, loops, and possibly related structures
## this changes the prefix with which the elements of that family are printed.
InstallMethod( SpecifyElmNamePrefix, "for collection and string",
[ IsCollection, IsString ],
function( Q, name )
local F;
F := FamilyObj( Representative( Q ) );
F!.elmNamePrefix := name;
end);
#############################################################################
##
#O BindElmNames( M )
##
## For each element e of the magma <M>, binds the identifier named String(e)
## to e.
## collection <C>. For quasigroups, loops, and possibly related structures
## this changes the prefix with which the elements of that family are printed.
InstallMethod( BindElmNames, "for a magma",
[ IsMagma ],
function( M )
local e, nm;
for e in Elements(M) do
nm := String(e);
BindGlobal(nm, e);
MakeReadWriteGlobal(nm);
od;
return;
end);
F := FamilyObj( Representative( Q ) );
F!.elmNamePrefix := name;
end);
#############################################################################
##
#O ConstructorFromTable( M )
##
## Given a magma <M>, returns a function which will create a domain of the
## same structure as M from from an operation table. This implementation of
## the method is to backfill the constructors for library domains that do
## not set the attribute directly at construction time. New domains that wish
## to use facilities like CanonicalCopy or Opposite should call
## SetConstructorFromTable at creation time.
InstallMethod( ConstructorFromTable, "for other magmas",
[ IsMagma ],
function ( M )
# Go in reverse order of refinement of structure
if IsGroup(M) then
return GroupByMultiplicationTable;
elif IsMagmaWithInverses(M) then
return MagmaWithInversesByMultiplicationTable;
elif IsMonoid(M) then
return MonoidByMultiplicationTable;
elif IsMagmaWithOne(M) then
return MagmaWithOneByMultiplicationTable;
elif IsSemigroup(M) then
return SemigroupByMultiplicationTable;
fi;
return MagmaByMultiplicationTable;
end);
#############################################################################
##
#O CanonicalCopy( Q )
##
## Returns a canonical copy of <Q>, that is, an isomorphic object <O> with
## canonical multiplication table and no parent set. Note that this is
## guaranteed to be a new object, not satisfying IsIdenticalObj with any
## previously existing structure. THEREFORE:
## (PROG) Properties and attributes are lost!
InstallMethod( CanonicalCopy, "for magma",
[ IsMagma ],
M -> ConstructorFromTable(M)(MultiplicationTable(M))
);
#############################################################################
## CREATING QUASIGROUPS AND LOOPS FROM A FILE
## -------------------------------------------------------------------------
#############################################################################
##
#F LOOPS_ReadCayleyTableFromFile( filename, replace_by_spaces )
##
## Auxiliary function. Reads the content of <filename> and tries to
## interpret the data as a multiplication table, according to the rules
## summarized below. If successful, it returns the multiplication table as
## an n by n array.
## ALGORITHM:
## 1) the content of the file is read into one string
## 2) all end-of-lines and all characters in the string <replace_by_spaces>
## are replaced by spaces
## 3) the string is split into chunks, where chunk = maximal substring
## without spaces
## 4) the number n of distinct chunks is found. If the number of chunks
## is not n^2, error is announced and function terminates
## 5) a numerical value 1 .. n is assigned to each chunk, depending on
## its position among the distinct chunks
## 6) multiplication table is constructed and returned
InstallGlobalFunction( LOOPS_ReadCayleyTableFromFile,
function( filename, replace_by_spaces)
local input, s, i, chunks, started, starting_pos, z, j, distinct_chunks, c, n, T;
if not ( IsString( filename) and IsString( replace_by_spaces ) ) then
Error( "LOOPS: <1> must be a file name, and <2> must be a string." );
fi;
input := InputTextFile( filename );
if input = fail then Error( "LOOPS: <1> is not a valid file name." ); fi;
s := ReadAll( input );
# removing end-of-lines, etc.
for i in [1..Length( s )] do
if (s[ i ] = '\n') or (s[ i ] in replace_by_spaces) then
s[ i ] := ' ';
fi;
od;
s[ Length( s ) + 1 ] := ' '; #to make sure that string ends with space
#parsing string into chunks separated by spaces
chunks := [];
started := false; starting_pos := 0;
for i in [1..Length( s )] do
if not started then
if not s[ i ] = ' ' then
started := true;
starting_pos := i;
fi;
else
if s[ i ] = ' ' then #end of chunk
z := "";
for j in [ starting_pos..i-1 ] do
z[ j - starting_pos + 1 ] := s[ j ];
od;
Add( chunks, z );
started := false;
fi;
fi;
od;
distinct_chunks := [];
for c in chunks do if not c in distinct_chunks then
Add( distinct_chunks, c );
fi; od;
n := Length( distinct_chunks );
if not Length( chunks ) = n^2 then
Error( "LOOPS: The data in the file cannot be arranged into a square table." );
fi;
T := List( [1..n], i -> 0*[1..n] );
for i in [1..n] do for j in [1..n] do
T[ i ][ j ] := Position( distinct_chunks, chunks[ (i-1)*n + j ] );
od; od;
return T;
end);
#############################################################################
##
#O QuasigroupFromFile( filename, replace] )
##
## Calls LOOPS_ReadCayleyTableFromFile( filename, replace ) in order to return
## the quasigroup with multiplication table in file <filename>.
InstallMethod( QuasigroupFromFile, "for string and string",
[ IsString, IsString ],
function( filename, replace )
return QuasigroupByCayleyTable( LOOPS_ReadCayleyTableFromFile( filename, replace ) );
end );
#############################################################################
##
#O LoopFromFile( filename , replace] )
##
## Calls LOOPS_ReadCayleyTableFromFile( filename, replace ) in order to return
## the loop with multiplication table in file <filename>.
InstallMethod( LoopFromFile, "for string and string",
[ IsString, IsString ],
function( filename, replace )
return LoopByCayleyTable( LOOPS_ReadCayleyTableFromFile( filename, replace ) );
end );
#############################################################################
## CREATING QUASIGROUPS AND LOOPS BY SECTIONS AND FOLDERS
## -------------------------------------------------------------------------
#############################################################################
##
#O CayleyTableByPerms( perms )
##
## Given a set <perms> of n permutations of an n-element set X, returns
## n by n Cayley table ct such that ct[i][j] = X[j]^perms[i].
## The operation is safe only if at most one permutation of <perms> is
## the identity permutation, and all other permutations of <perms>
## move all points of X.
InstallMethod( CayleyTableByPerms,
"for a list of permutations",
[ IsPermCollection ],
function( perms )
local n, pts, max;
n := Length( perms );
if n=1 then
return [ [ 1 ] ];
fi;
# one of perms[ 1 ], perms[ 2 ] must move all points
pts := MovedPoints( perms[ 2 ] );
if pts = [] then
pts := MovedPoints( perms[ 1 ] );
fi;
max := Maximum( pts );
# we permute the whole interval [1..max] and then keep only those coordinates corresponding to pts
return List( perms, p -> Permuted( [1..max], p^(-1) ){ pts } );
end);
#############################################################################
##
#O QuasigroupByLeftSection( sect )
##
## Returns the quasigroup whose left section is the list of permutations
## <sect>.
InstallMethod( QuasigroupByLeftSection,
"for a set of left translation maps",
[ IsPermCollection ],
function( sect )
return QuasigroupByCayleyTable( CayleyTableByPerms( sect ) );
end);
#############################################################################
##
#O LoopByLeftSection( sect )
##
## Returns the loop whose left section is the list of permutations <sect>.
## Since the order of translations in <sect> is determined by their
## image of the neutral element 1, we disregard the order.
InstallMethod( LoopByLeftSection,
"for a set of left translation maps",
[ IsPermCollection ],
function( sect )
return LoopByCayleyTable( Set ( CayleyTableByPerms( sect ) ) );
end);
#############################################################################
##
#O QuasigroupByRightSection( sect )
##
## Returns the quasigroup whose right section is the list of permutations
## <sect>.
InstallMethod( QuasigroupByRightSection,
"for a set of left translation maps",
[ IsPermCollection ],
function( sect )
return QuasigroupByCayleyTable( TransposedMat ( CayleyTableByPerms( sect ) ) );
end);
#############################################################################
##
#O LoopByRightSection( sect )
##
## Returns the loop whose right section is the list of permutations <sect>.
## Since the order of translations in <sect> is determined by their
## image of the neutral element 1, we disregard the order.
InstallMethod( LoopByRightSection,
"for a set of left translation maps",
[ IsPermCollection ],
function( sect )
return LoopByCayleyTable( TransposedMat ( Set ( CayleyTableByPerms( sect ) ) ) );
end);
#############################################################################
##
#O LOOPS_CayleyTableByRightFolder( G, H, T )
##
## Auxiliary operation.
##
## A right folder is a triple (G,H,T) such that G is a group, H is
## a subgroup of G, and T is a right transversal to H in G.
##
## Returns the multiplication table on {Hx: x in G} by Ht*Hs = H(ts).
##
## The multiplication table is a quasigroup if and only if
## T is a right transversal to every conjugate H^g in G.
InstallGlobalFunction( LOOPS_CayleyTableByRightFolder,
function( G, H, T )
local act, nT, actT, i, p, ct;
# act = action of G on right cosest G/H
act := ActionHomomorphism( G, RightCosets( G, H ), OnRight );
nT := Length( T );
# actT = permutations on G/H induced by elements of T
actT := [1..nT];
for i in [1..nT] do
actT[ i ] := T[ i ]^act;
od;
# the order of right cosets determined by T might not agree with the default order of right cosets ...
p := PermList( List( [1..nT], i -> 1^actT[ i ] ) );
ct := List( [1..nT], i -> ListPerm( p * actT[ i ] * p^(-1) ) );
for i in [1..nT] do
if ct[ i ] = [] then # this can happen since ListPerm( () ) = []
ct[ i ] := [1..nT];
fi;
od;
return TransposedMat( ct );
end);
#############################################################################
##
#O QuasigroupByRightFolder( G, H, T )
##
## See CayleyTableByRightFolder. We do not check if the right folder
## is a quasigroup right folder.
InstallMethod( QuasigroupByRightFolder,
"for a group, a subgroup and right transversal",
[ IsGroup, IsGroup, IsMultiplicativeElementCollection ],
function( G, H, T )
return QuasigroupByCayleyTable( LOOPS_CayleyTableByRightFolder( G, H, T ) );
end);
#############################################################################
##
#O LoopByRightFolder( G, H, T )
##
## See CayleyTableByRigthFolder. We do not check if the right folder
## is a loop right folder.
InstallOtherMethod( LoopByRightFolder,
"for a group, a subgroup and right transversal",
[ IsGroup, IsGroup, IsMultiplicativeElementCollection ],
function( G, H, T )
return LoopByCayleyTable( LOOPS_CayleyTableByRightFolder( G, H, T ) );
end);
#############################################################################
## CONVERSIONS
## -------------------------------------------------------------------------
#############################################################################
##
#O IntoQuasigroup( M )
##
## Given a magma, returns the corresponding quasigroup, if possible.
InstallMethod( IntoQuasigroup, "for magma",
[ IsMagma ],
function( M )
local ct;
if IsQuasigroup( M ) then # leave quasigroups and loops intact
return M;
fi;
# magma, not necessarily a quasigroup
ct := MultiplicationTable( Elements( M ) );
if IsQuasigroupTable( ct ) then
return QuasigroupByCayleyTable( ct );
fi;
return fail;
end);
#############################################################################
##
#O PrincipalLoopIsotope( Q, f, g )
##
## Let Q be a quasigroup and f, g elements of Q.
## Define new operation on Q by x+y = R^{-1}(g)(x) * L^{-1}(f)(y).
## Then (Q,+) is a loop with neutral element f*g.
## We return isomorphic copy of (Q,+) via the isomorphism (1,f*g).
InstallMethod( PrincipalLoopIsotope,
"for quasigroup and two quasigroup elements",
[ IsQuasigroup, IsQuasigroupElement, IsQuasigroupElement ],
function( Q, f, g )
local n, L, R, i, j, ct, p;
if not (f in Q and g in Q) then
Error("LOOPS: <2> and <3> must be elements of quasigroup <1>.");
fi;
# constructing new multiplication
n := Size( Q );
ct := List( [1..n], i -> [1..n] );
L := Inverse( LeftTranslation( Q, f ) ); # inverse of left translation by f
R := Inverse( RightTranslation( Q, g ) ); # inverse or right translation by g
for i in [1..n] do for j in [1..n] do
ct[ i ][ j ] := CayleyTable( Q )[ i^R ][ j^L ];
od; od;
# the neutral element of ct is now f*g. We apply isomorphism (1, f*g).
p := Position(Q, f*g);
if p>1 then
p := (1, p); # note that p is its own inverse
ct := List([1..n], i-> List([1..n], j -> ( ct[ i^p ][ j^p ] )^p ) );
fi;
return LoopByCayleyTable( ct );
end);
#############################################################################
##
#O IntoLoop( M )
##
## Given a magma, returns the corresponding loop, if possible.
InstallMethod( IntoLoop, "for magma",
[ IsMagma ],
function( M )
local e, p, ct;
if IsLoop( M ) then # loops are left intact
return M;
fi;
# magma, not necessarily a loop
M := IntoQuasigroup( M );
if M = fail then
return fail;
fi;
# quasigroup, not necesarily a loop
e := MultiplicativeNeutralElement( M );
if e = fail then # no neutral element, use principal isotope
return PrincipalLoopIsotope( M, Elements( M )[ 1 ], Elements( M )[ 1 ] );
fi;
# quasigroup with neutral element, i.e., a loop
p := Position( M, e );
if p>1 then
p := (1,p); # note that p is its own inverse
ct := List([1..Size(M)], i-> List([1..Size(M)], j ->
( CayleyTable( M )[ i^p ][ j^p ] )^p
) );
else
ct := CayleyTable( M );
fi;
return LoopByCayleyTable( ct );
end );
#############################################################################
##
#O IntoGroup( M )
##
## Given a magma <M>, returns the corresponding group, if possible.
InstallOtherMethod( IntoGroup, "for magma",
[ IsMagma ],
function( M )
if IsGroup( M ) then # groups are left intact
return M;
fi;
# magma, not necessarily a group
M := IntoLoop( M );
if M=fail or (not IsAssociative( M ) ) then
return fail;
fi;
# group
return RightMultiplicationGroup( M );
end);
#############################################################################
## PRODUCTS OF QUASIGROUPS AND LOOPS
## -------------------------------------------------------------------------
#############################################################################
##
#F DirectProduct( Q1, Q2, ..., Qn )
##
## Returns the direct product of quasigroups <Q1>, <Q2>, ... , <Qn>.
## The quasigroups can be declared as quasigroups, loops or groups.
# The following is necessary due to implementation of DirectProduct for
# groups in GAP. The idea is as follows:
# We want to calculate direct product of quasigroups, loops and groups.
# If only groups are on the list, standard GAP DirectProduct will take care
# of it. If there are also some quasigroups or loops on the list,
# we must take care of it.
# However, we do not know if such a list will be processed with
# DirectProductOp( <IsList>, <IsGroup> ), or
# DirectProductOp( <IsList>, <IsQuasigroup> ),
# since this depends on which algebra is listed first.
# We therefore take care of both situations.
InstallOtherMethod( DirectProductOp, "for DirectProduct( <IsList>, <IsGroup> )",
[ IsList, IsGroup],
function( list, first )
local L, p;
# Check the arguments.
if IsEmpty( list ) then Error( "LOOPS: <1> must be nonempty." ); fi;
if not ForAny( list, IsQuasigroup ) then
# there are no quasigroups or loops on the list
TryNextMethod();
fi;
if ForAny( list, G -> (not IsGroup( G )) and (not IsQuasigroup( G ) ) ) then
# there are other objects beside groups, loops and quasigroups on the list
TryNextMethod();
fi;
# all arguments are groups, quasigroups or loops, and there is at least one loop
# making sure that a loop is listed first so that this method is not called again
for L in list do
if not IsGroup( L ) then
p := Position( list, L );
list[ 1 ] := L;
list[ p ] := first;
break;
fi;
od;
return DirectProductOp( list, list[ 1 ] );
end);
InstallOtherMethod( DirectProductOp, "for DirectProduct( <IsList>, <IsQuasigroup> )",
[ IsList, IsQuasigroup ],
function( list, dummy )
local group_list, quasigroup_list, group_product, are_all_loops,
n, i, nL, nM, TL, TM, T, j, k, s;
# check the arguments
if IsEmpty( list ) then
Error( "LOOPS: <1> must be nonempty." );
elif ForAny( list, G -> (not IsGroup( G )) and (not IsQuasigroup( G ) ) ) then
TryNextMethod();
fi;
# only groups, quasigroups and loops are on the list, with at least one non-group
group_list := Filtered( list, G -> IsGroup( G ) );
quasigroup_list := Filtered( list, G -> IsQuasigroup( G ) );
if not IsEmpty( group_list ) then # some groups are on the list
group_product := DirectProductOp( group_list, group_list[ 1 ] );
Add( quasigroup_list, IntoLoop( group_product ) );
fi;
# keeping track of whether all algebras are in fact loops
are_all_loops := ForAll( quasigroup_list, IsLoop );
# now only quasigroups and loops are on the list
n := Length( quasigroup_list );
if n=1 then
return quasigroup_list[ 1 ];
fi;
# at least 2 quasigroups and loops; we will not use recursion
# making all Cayley tables canonical
for s in [1..n] do
quasigroup_list[ s ] :=
CanonicalCayleyTableOfLeftQuasigroupTable(
CayleyTable( quasigroup_list[ s ] ) );
od;
# At this point the entries in quasigroup_list are really just tables
for s in [2..n] do
nL := Length( quasigroup_list[ 1 ] );
nM := Length( quasigroup_list[ s ] );
TL := quasigroup_list[ 1 ];
TM := quasigroup_list[ s ];
T := List( [1..nL*nM], j->[] );
# not efficient, but it does the job
for i in [1..nM] do for j in [1..nM] do for k in [1..nL] do
Append( T[ (i-1)*nL + k ], TL[ k ] + nL*(TM[i][j]-1) );
od; od; od;
quasigroup_list[ 1 ] := T;
od;
if are_all_loops then
return LoopByCayleyTable( quasigroup_list[1] );
fi;
return QuasigroupByCayleyTable( quasigroup_list[1] );
end );
#############################################################################
## OPPOSITE QUASIGROUPS AND LOOPS
## --------------------------------------------------------------------------
#############################################################################
##
#O OppositeQuasigroup( Q )
##
## Identical to Opposite, except forces its return to be a quasigroup if
## possible
InstallGlobalFunction( OppositeQuasigroup,
Q -> IntoQuasigroup( Opposite( Q ) ) );
#############################################################################
##
#O OppositeLoop( Q )
##
## Identical to Opposite, except forces its return to be a loop if possible
InstallGlobalFunction( OppositeLoop, L -> IntoLoop( Opposite( L ) ) );
#############################################################################
##
#A Opposite( M )
##
## Returns the magma opposite to the magma <M>, with as much structure
## as can be preserved.
InstallMethod( Opposite, "for magma",
[ IsMagma ],
M -> ConstructorFromTable(M)( TransposedMat( MultiplicationTable( M ) ) )
);
#############################################################################
## DISPLAYING QUASIGROUPS AND LOOPS
## -------------------------------------------------------------------------
InstallMethod( ViewObj, "for quasigroup",
[ IsQuasigroup ],
function( Q )
Print( "<quasigroup of order ", Size( Q ), ">" );
end );
## dangerous for large quasigroups
InstallMethod( PrintObj, "for quasigroup",
[ IsQuasigroup ],
function( Q )
if HasCayleyTable( Q ) then
Print( "<quasigroup with multiplication table\n" );
PrintArray( CayleyTable( Q ) );
else
Print( "<quasigroup with elements\n" );
Print( Elements( Q ) );
fi;
Print( ">\n" );
end );
InstallMethod( ViewObj, "for loop",
[ IsLoop ],
function( L )
if HasIsAssociative( L ) and IsAssociative( L ) then
Print( "<associative loop of order ", Size( L ), ">");
elif HasIsExtraLoop( L ) and IsExtraLoop( L ) then
Print( "<extra loop of order ", Size( L ), ">");
elif HasIsMoufangLoop( L ) and IsMoufangLoop( L ) then
Print( "<Moufang loop of order ", Size( L ), ">");
elif HasIsCLoop( L ) and IsCLoop( L ) then
Print( "<C loop of order ", Size( L ), ">");
elif HasIsLeftBolLoop( L ) and IsLeftBolLoop( L ) then
Print( "<left Bol loop of order ", Size( L ), ">");
elif HasIsRightBolLoop( L ) and IsRightBolLoop( L ) then
Print( "<right Bol loop of order ", Size( L ), ">");
elif HasIsLCLoop( L ) and IsLCLoop( L ) then
Print( "<LC loop of order ", Size( L ), ">");
elif HasIsRCLoop( L ) and IsRCLoop( L ) then
Print( "<RC loop of order ", Size( L ), ">");
elif HasIsLeftAlternative( L ) and IsLeftAlternative( L ) then
if HasIsRightAlternative( L ) and IsRightAlternative( L ) then
Print( "<alternative loop of order ", Size( L ), ">");
else
Print( "<left alternative loop of order ", Size( L ), ">");
fi;
elif HasIsRightAlternative( L ) and IsRightAlternative( L ) then
Print( "<right alternative loop of order ", Size( L ), ">");
elif HasIsFlexible( L ) and IsFlexible( L ) then
Print( "<flexible loop of order ", Size( L ), ">");
else
# MORE ??
Print( "<loop of order ", Size( L ), ">" );
fi;
end );
## dangerous for large loops
InstallMethod( PrintObj, "for loop",
[ IsLoop ],
function( L )
if HasCayleyTable( L ) then
Print( "<loop with multiplication table\n" );
PrintArray( CayleyTable( L ) );
else
Print( "<loop with elements\n" );
Print( Elements( L ) );
fi;
Print( ">\n" );
end );
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