HomalgMorphism.gi
#############################################################################
##
## HomalgMorphism.gi homalg package Mohamed Barakat
##
## Copyright 2007-2010, Mohamed Barakat, University of Kaiserslautern
##
## Implementation for morphisms of (Abelian) categories.
##
#############################################################################
####################################
#
# representations:
#
####################################
## <#GAPDoc Label="IsMorphismOfFinitelyGeneratedObjectsRep">
## <ManSection>
## <Filt Type="Representation" Arg="phi" Name="IsMorphismOfFinitelyGeneratedObjectsRep"/>
## <Returns><C>true</C> or <C>false</C></Returns>
## <Description>
## The &GAP; representation of morphisms of finitley generated &homalg; objects. <P/>
## (It is a representation of the &GAP; category <Ref Filt="IsHomalgMorphism"/>.)
## <Listing Type="Code"><![CDATA[
DeclareRepresentation( "IsMorphismOfFinitelyGeneratedObjectsRep",
IsHomalgMorphism,
[ ] );
## ]]></Listing>
## </Description>
## </ManSection>
## <#/GAPDoc>
## <#GAPDoc Label="IsStaticMorphismOfFinitelyGeneratedObjectsRep">
## <ManSection>
## <Filt Type="Representation" Arg="phi" Name="IsStaticMorphismOfFinitelyGeneratedObjectsRep"/>
## <Returns><C>true</C> or <C>false</C></Returns>
## <Description>
## The &GAP; representation of static morphisms of finitley generated &homalg; static objects. <P/>
## (It is a representation of the &GAP; category <Ref Filt="IsHomalgStaticMorphism"/>,
## which is a subrepresentation of the &GAP; representation
## <Ref Filt="IsMorphismOfFinitelyGeneratedObjectsRep"/>.)
## <Listing Type="Code"><![CDATA[
DeclareRepresentation( "IsStaticMorphismOfFinitelyGeneratedObjectsRep",
IsHomalgStaticMorphism and
IsMorphismOfFinitelyGeneratedObjectsRep,
[ ] );
## ]]></Listing>
## </Description>
## </ManSection>
## <#/GAPDoc>
####################################
#
# methods for operations:
#
####################################
##
InstallMethod( homalgResetFilters,
"for homalg static morphisms",
[ IsHomalgStaticMorphism ],
function( phi )
local property;
for property in LIMOR.intrinsic_properties do
ResetFilterObj( phi, ValueGlobal( property ) );
od;
end );
##
InstallMethod( HomalgCategory,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
return HomalgCategory( Source( phi ) );
end );
##
InstallMethod( StructureObject,
"for homalg morphism",
[ IsHomalgMorphism ],
function( phi )
return StructureObject( Source( phi ) );
end );
##
InstallMethod( AreComparableMorphisms,
"for homalg morphisms",
[ IsHomalgMorphism, IsHomalgMorphism ],
function( phi1, phi2 )
return IsIdenticalObj( Source( phi1 ), Source( phi2 ) ) and
IsIdenticalObj( Range( phi1 ), Range( phi2 ) );
end );
##
InstallMethod( AreComposableMorphisms,
"for homalg morphisms",
[ IsHomalgMorphism and IsHomalgRightObjectOrMorphismOfRightObjects,
IsHomalgMorphism and IsHomalgRightObjectOrMorphismOfRightObjects ],
function( phi2, phi1 )
if IsHomalgChainMorphism( phi1 ) and IsHomalgChainMorphism( phi2 ) then
return Range( phi1 ) = Source( phi2 );
fi;
return IsIdenticalObj( Range( phi1 ), Source( phi2 ) );
end );
##
InstallMethod( AreComposableMorphisms,
"for homalg morphisms",
[ IsHomalgMorphism and IsHomalgLeftObjectOrMorphismOfLeftObjects,
IsHomalgMorphism and IsHomalgLeftObjectOrMorphismOfLeftObjects ],
function( phi1, phi2 )
if IsHomalgChainMorphism( phi1 ) and IsHomalgChainMorphism( phi2 ) then
return Range( phi1 ) = Source( phi2 );
fi;
return IsIdenticalObj( Range( phi1 ), Source( phi2 ) );
end );
## a synonym of `-<elm>':
InstallMethod( AdditiveInverseMutable,
"of homalg morphisms",
[ IsHomalgMorphism and IsZero ],
function( phi )
return phi;
end );
##
InstallMethod( AssociatedMorphism,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
local psi;
if not HasMorphismAid( phi ) then
return phi;
fi;
psi := PreCompose( phi, CokernelEpi( MorphismAid( phi ) ) );
Assert( 6, not HasMorphismAid( psi ) or IsZero( MorphismAid( psi ) ) );
if HasMorphismAid( psi ) then
psi := RemoveMorphismAid( psi );
fi;
return psi;
end );
##
InstallMethod( GetMorphismAid,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
local aid;
if not HasMorphismAid( phi ) then
Error( "the morphism does not have a morphism aid" );
fi;
aid := phi!.MorphismAid;
# This is the "classical" aid:
if IsHomalgMorphism( aid ) and IsIdenticalObj( Range( phi ), Range( aid ) ) then
return aid;
# PostDivide saves a (list of a) morphism which has the correct aid as the kernel.
# we get the correct information here:
elif IsList( aid ) and Length( aid ) = 1 and IsHomalgMorphism( aid[1] ) and IsIdenticalObj( Range( phi ), Source( aid[1] ) ) then
aid := KernelSubobject( aid[1] )!.map_having_subobject_as_its_image;
SetMorphismAid( phi, aid );
return aid;
else
Error( "the morphism has an unknown object as morphism aid" );
fi;
end );
##
InstallMethod( \=,
"for two comparable homalg static morphisms",
[ IsHomalgStaticMorphism, IsHomalgStaticMorphism ], 10001,
function( phi1, phi2 )
if not AreComparableMorphisms( phi1, phi2 ) then
return false;
fi;
TryNextMethod( );
end );
##
InstallMethod( \=,
"for two comparable homalg static morphisms",
[ IsHomalgStaticMorphism and HasMorphismAid, IsHomalgStaticMorphism ], 1001,
function( phi1, phi2 )
local pi;
## AreComparableMorphisms is tested in a high ranked method above
if HasMorphismAid( phi2 ) then
TryNextMethod( );
fi;
if not IsZero( MorphismAid( phi1 ) ) then
return false;
fi;
pi := CokernelEpi( MorphismAid( phi1 ) );
return RemoveMorphismAid( PreCompose( phi1, pi ) ) = PreCompose( phi2, pi );
end );
##
InstallMethod( \=,
"for two comparable homalg static morphisms",
[ IsHomalgStaticMorphism, IsHomalgStaticMorphism and HasMorphismAid ], 2001,
function( phi1, phi2 )
local pi;
## AreComparableMorphisms is tested in a high ranked method above
if ( not IsZero( MorphismAid( phi2 ) ) and not HasMorphismAid( phi1 ) ) or
( HasMorphismAid( phi1 ) and not ( ImageSubobject( MorphismAid( phi1 ) ) = ImageSubobject( MorphismAid( phi2 ) ) ) ) then
return false;
fi;
pi := CokernelEpi( MorphismAid( phi2 ) );
return RemoveMorphismAid( PreCompose( phi1, pi ) ) = RemoveMorphismAid( PreCompose( phi2, pi ) );
end );
##
InstallMethod( \=,
"for two comparable homalg maps",
[ IsHomalgStaticMorphism, IsHomalgStaticMorphism ],
function( phi1, phi2 )
local phi;
## should be obsolete by the high ranked method above
if HasMorphismAid( phi1 ) then
TryNextMethod( );
elif HasMorphismAid( phi2 ) then
TryNextMethod( );
fi;
phi := phi1- phi2;
return IsZero( phi );
end );
##
## composition is a bifunctor to profit from the caching mechanisms for functors (cf. ToolFunctors.gi)
##
##
InstallMethod( POW,
"for homalg morphisms",
[ IsHomalgMorphism, IsInt ],
function( phi, pow )
local id, inv;
if pow = -1 then
id := TheIdentityMorphism( Range( phi ) );
inv := id / phi; ## mimic lift
if HasIsIsomorphism( phi ) then
SetIsIsomorphism( inv, IsIsomorphism( phi ) );
fi;
## CAUTION: inv might very well be non-well-defined
return inv;
fi;
TryNextMethod( );
end );
## <#GAPDoc Label="ByASmallerPresentation:morphism">
## <ManSection>
## <Meth Arg="phi" Name="ByASmallerPresentation" Label="for morphisms"/>
## <Returns>a &homalg; map</Returns>
## <Description>
## It invokes <C>ByASmallerPresentation</C> for &homalg; (static) objects.
## <Listing Type="Code"><![CDATA[
InstallMethod( ByASmallerPresentation,
"for homalg morphisms",
[ IsStaticMorphismOfFinitelyGeneratedObjectsRep ],
function( phi )
ByASmallerPresentation( Source( phi ) );
ByASmallerPresentation( Range( phi ) );
return DecideZero( phi );
end );
## ]]></Listing>
## This method performs side effects on its argument <A>phi</A> and returns it.
## <Example><![CDATA[
## gap> ZZ := HomalgRingOfIntegers( );
## Z
## gap> M := HomalgMatrix( "[ 2, 3, 4, 5, 6, 7 ]", 2, 3, ZZ );
## <A 2 x 3 matrix over an internal ring>
## gap> M := LeftPresentation( M );
## <A non-torsion left module presented by 2 relations for 3 generators>
## gap> N := HomalgMatrix( "[ 2, 3, 4, 5, 6, 7, 8, 9 ]", 2, 4, ZZ );
## <A 2 x 4 matrix over an internal ring>
## gap> N := LeftPresentation( N );
## <A non-torsion left module presented by 2 relations for 4 generators>
## gap> mat := HomalgMatrix( "[ \
## > 1, 0, -2, -4, \
## > 0, 1, 4, 7, \
## > 1, 0, -2, -4 \
## > ]", 3, 4, ZZ );
## <A 3 x 4 matrix over an internal ring>
## gap> phi := HomalgMap( mat, M, N );
## <A "homomorphism" of left modules>
## gap> IsMorphism( phi );
## true
## gap> phi;
## <A homomorphism of left modules>
## gap> Display( phi );
## [ [ 1, 0, -2, -4 ],
## [ 0, 1, 4, 7 ],
## [ 1, 0, -2, -4 ] ]
##
## the map is currently represented by the above 3 x 4 matrix
## gap> ByASmallerPresentation( phi );
## <A non-zero homomorphism of left modules>
## gap> Display( phi );
## [ [ 0, 0, 0 ],
## [ 1, -1, -2 ] ]
##
## the map is currently represented by the above 2 x 3 matrix
## gap> M;
## <A rank 1 left module presented by 1 relation for 2 generators>
## gap> Display( M );
## Z/< 3 > + Z^(1 x 1)
## gap> N;
## <A rank 2 left module presented by 1 relation for 3 generators>
## gap> Display( N );
## Z/< 4 > + Z^(1 x 2)
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
## this should be the lowest rank method
InstallMethod( PreInverse,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
return fail;
end );
## this should be the lowest rank method
InstallMethod( PostInverse,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
return fail;
end );
#=======================================================================
# Complete an image-square
#
# A_ is a free or beta1 is injective ( cf. [HS, Lemma III.3.1]
# and [BR08, Subsection 3.1.2] )
#
# A_ --(alpha1)--> A
# | |
# (psi=?) Sq1 (phi)
# | |
# v v
# B_ --(beta1)---> B
#
#_______________________________________________________________________
##
InstallMethod( CompleteImageSquare, ### defines: CompleteImageSquare (CompleteImSq)
"for homalg morphisms",
[ IsHomalgMorphism,
IsHomalgMorphism,
IsHomalgMorphism ],
function( alpha1, phi, beta1 )
return PreCompose( alpha1, phi ) / beta1; ## lift or projective lift
end );
#=======================================================================
# Complete a kernel-square
#
# alpha2 is surjective ( cf. [HS, Lemma III.3.1] )
#
# A --(alpha2)->> _A
# | |
# (phi) Sq2 (theta=?)
# | |
# v v
# B --(beta2)---> _B
#
#_______________________________________________________________________
##
InstallMethod( CompleteKernelSquare, ### defines: CompleteKernelSquare
"for homalg morphisms",
[ IsHomalgMorphism,
IsHomalgMorphism,
IsHomalgMorphism ],
function( alpha2, phi, beta2 )
return PreDivide( alpha2, PreCompose( phi, beta2 ) ); ## colift
end );
## this is equivalent to DirectSum( phi1, phi2 )
## DirectSum of two morhisms is installed by a universal method for functors
## DiagonalMorphism is specific to the DirectSum functor
InstallMethod( DiagonalMorphismOp,
"for two homalg morphisms",
[ IsHomalgMorphism, IsHomalgMorphism ],
function( phi1, phi2 )
local zero_M1_N2, zero_M2_N1, phi1_0, phi2_0, phi;
zero_M1_N2 := TheZeroMorphism( Source( phi1 ), Range( phi2 ) );
zero_M2_N1 := TheZeroMorphism( Source( phi2 ), Range( phi1 ) );
phi1_0 := ProductMorphism( phi1, zero_M1_N2 );
phi2_0 := ProductMorphism( zero_M2_N1, phi2 );
phi := CoproductMorphism( phi1_0, phi2_0 );
if HasIsMonomorphism( phi1 ) and HasIsMonomorphism( phi2 ) then
SetIsMonomorphism( phi, IsMonomorphism( phi1 ) and IsMonomorphism( phi2 ) );
elif HasIsMorphism( phi1 ) and HasIsMorphism( phi2 ) then
SetIsMorphism( phi, IsMorphism( phi1 ) and IsMorphism( phi2 ) );
fi;
if HasIsEpimorphism( phi1 ) and HasIsEpimorphism( phi2 ) then
SetIsEpimorphism( phi, IsEpimorphism( phi1 ) and IsEpimorphism( phi2 ) );
fi;
SetDirectSummands( phi, [ phi1, phi2 ] );
return phi;
end );
## the second argument is there for method selection
InstallMethod( DiagonalMorphismOp,
"for a list of homalg morphims and a single one",
[ IsList, IsHomalgMorphism ],
function( L, phi )
return Iterated( L, DiagonalMorphismOp );
end );
##
InstallGlobalFunction( DiagonalMorphism,
function ( arg )
local d;
if Length( arg ) = 0 then
Error( "<arg> must be nonempty" );
elif Length( arg ) = 1 and IsList( arg[1] ) then
if IsEmpty( arg[1] ) then
Error( "<arg>[1] must be nonempty" );
fi;
arg := arg[1];
fi;
return DiagonalMorphismOp( arg, arg[1] );
end );
## this should be the lowest rank method
InstallMethod( UpdateObjectsByMorphism,
"for homalg morphisms",
[ IsHomalgMorphism ],
function( phi )
## fallback: do nothing :)
end );
##
InstallMethod( UpdateObjectsByMorphism,
"for homalg morphisms",
[ IsHomalgMorphism and IsIsomorphism ],
function( phi )
if HasIsZero( Source( phi ) ) or HasIsZero( Range( phi ) ) then
IsZero( phi );
fi;
MatchPropertiesAndAttributes( Source( phi ), Range( phi ), LIMOR.intrinsic_properties, LIMOR.intrinsic_attributes );
end );
####################################
#
# constructors
#
####################################
##
InstallMethod( \*,
"for a structure object and a static morphism",
[ IsStructureObject, IsHomalgStaticMorphism ],
function( R, phi )
return BaseChange( R, phi );
end );
##
InstallMethod( \*,
"for a static morphism and a structure object",
[ IsHomalgStaticMorphism, IsStructureObject ],
function( phi, R )
return R * phi;
end );
####################################
#
# View, Print, and Display methods:
#
####################################
##
InstallMethod( ViewObj,
"for homalg maps",
[ IsHomalgMorphism ],
function( o )
local s, S;
s := " ";
S := Source( o );
if IsBound( S!.adjective ) then
s := Concatenation( s, S!.adjective, " " );
fi;
if IsHomalgLeftObjectOrMorphismOfLeftObjects( o ) then
s := Concatenation( s, "left " );
else
s := Concatenation( s, "right " );
fi;
if IsHomalgEndomorphism( o ) then
if IsBound( S!.string ) then
s := Concatenation( s, S!.string );
else
s := Concatenation( s, "object" );
fi;
else
if IsBound( S!.string_plural ) then
s := Concatenation( s, S!.string_plural );
elif IsBound( S!.string ) then
s := Concatenation( s, S!.string, "s" );
else
s := Concatenation( s, "objects" );
fi;
fi;
s := Concatenation( ViewString( o ), s, ">" );
if ( HasIsOne( o ) and IsOne( o ) ) or ( HasIsZero( o ) and IsZero( o ) and not HasMorphismAid( o ) ) then
Print( "<The ", s );
elif s[1] in "aeiouAEIOU" then
Print( "<An ", s );
elif s[1] in "\"" and s[2] in "aeiouAEIOU" then
Print( "<An ", s );
else
Print( "<A ", s );
fi;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism ],
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
if HasIsMorphism( o ) then
if IsMorphism( o ) then
s := Concatenation( s, "homomorphism of" );
elif HasMorphismAid( o ) then ## otherwise the notion of generalized morphism is meaningless
if HasIsGeneralizedMorphism( o ) then
if HasIsGeneralizedIsomorphism( o ) and IsGeneralizedIsomorphism( o ) then
s := Concatenation( s, "generalized isomorphism of" );
elif HasIsGeneralizedMonomorphism( o ) and IsGeneralizedMonomorphism( o ) then
s := Concatenation( s, "generalized embedding of" );
elif HasIsGeneralizedEpimorphism( o ) and IsGeneralizedEpimorphism( o ) then
s := Concatenation( s, "generalized epimorphism of" );
elif IsGeneralizedMorphism( o ) then
s := Concatenation( s, "generalized homomorphism of" );
else
s := Concatenation( s, "non-well defined (generalized) map of" );
fi;
else
s := Concatenation( s, "\"generalized homomorphism\" of" );
fi;
else
s := Concatenation( s, "non-well-defined map between" );
fi;
else
if HasMorphismAid( o ) then ## otherwise the notion of generalized morphism is meaningless
if HasIsGeneralizedMorphism( o ) then
if HasIsGeneralizedIsomorphism( o ) and IsGeneralizedIsomorphism( o ) then
s := Concatenation( s, "generalized isomorphism of" );
elif HasIsGeneralizedMonomorphism( o ) and IsGeneralizedMonomorphism( o ) then
s := Concatenation( s, "generalized embedding of" );
elif HasIsGeneralizedEpimorphism( o ) and IsGeneralizedEpimorphism( o ) then
s := Concatenation( s, "generalized epimorphism of" );
elif IsGeneralizedMorphism( o ) then
s := Concatenation( s, "generalized homomorphism of" );
else
s := Concatenation( s, "non-well defined (generalized) map of" );
fi;
else
s := Concatenation( s, "\"generalized homomorphism\" of" );
fi;
else
s := Concatenation( s, "\"homomorphism\" of" );
fi;
fi;
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsMonomorphism ], 896,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "monomorphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsEpimorphism ], 897,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "epimorphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsSplitMonomorphism ], 1998,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "split monomorphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsSplitEpimorphism ], 1999,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "split epimorphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsIsomorphism ], 2000,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "isomorphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsZero ], 2001,
function( o )
local s;
s := "";
if HasMorphismAid( o ) then
s := Concatenation( s, "zero generalized " );
else
s := Concatenation( s, "zero " );
fi;
s := Concatenation( s, "morphism of" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgMorphism and IsIsomorphism and IsZero ], 2003,
function( o )
return "zero morphism of zero";
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism ],
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
if HasIsMorphism( o ) then
if IsMorphism( o ) then
s := Concatenation( s, "endomorphism of" );
else
s := Concatenation( s, "non-well-defined self-map of" );
fi;
else
s := Concatenation( s, "endo\"morphism\" of" );
fi;
return Concatenation( s, " a" );
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsIdempotent ],
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
if HasIsOne( o ) and not IsOne( o ) then
s := Concatenation( s, "nontrivial " );
else
s := Concatenation( s, "non-zero " );
fi;
elif HasIsOne( o ) and not IsOne( o ) then
s := Concatenation( s, "non-identity " );
fi;
if HasIsMorphism( o ) then
if IsMorphism( o ) then
s := Concatenation( s, "idempotent of" );
else
s := Concatenation( s, "non-well-defined self-map of" );
fi;
else
s := Concatenation( s, "\"idempotent\" of" );
fi;
return Concatenation( s, " a" );
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsMonomorphism ],
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
return Concatenation( s, "monic endomorphism of a" );
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsEpimorphism ], 996,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
return Concatenation( s, "epic endomorphism of a" );
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsSplitMonomorphism ], 997,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
return Concatenation( s, "split monic endomorphism of a" );
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsSplitEpimorphism ], 2998,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "split epic endomorphism of a" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsAutomorphism ], 2999,
function( o )
local s;
s := "";
## if this method applies and HasIsZero is set we already
## know that o is a non-zero morphism of homalg objects
if HasIsZero( o ) and not IsZero( o ) then
s := Concatenation( s, "non-zero " );
fi;
s := Concatenation( s, "automorphism of a" );
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsOne ], 5000,
function( o )
local s;
s := "identity morphism of a";
if HasIsZero( Source( o ) ) and not IsZero( Source( o ) ) then
s := Concatenation( s, " non-zero" );
fi;
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsZero ], 5001,
function( o )
local s;
s := "zero endomorphism of a";
if HasIsZero( Source( o ) ) and not IsZero( Source( o ) ) then
s := Concatenation( s, " non-zero" );
fi;
return s;
end );
##
InstallMethod( ViewString,
"for homalg maps",
[ IsHomalgEndomorphism and IsAutomorphism and IsZero ], 3003,
function( o )
return "zero endomorphism of a zero";
end );
