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Fix: Isomorphisms of trivial groups are bijective #1116

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Feb 2, 2017
Merged

Fix: Isomorphisms of trivial groups are bijective #1116

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afad0d9
Fix: Isomorphisms of trivial groups are bijective
Feb 2, 2017
4d493ac
Add test for isomorphism of trivial groups
Feb 2, 2017
7d16e9f
Add test for inverse of iso of trivial groups
Feb 2, 2017
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4 changes: 3 additions & 1 deletion lib/ghom.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -1402,7 +1402,9 @@ BindGlobal( "IsomorphismAbelianGroupViaIndependentGenerators", function ( filter

if IsTrivial( G ) then
K := TrivialGroup( filter );
return GroupHomomorphismByImagesNC( G, K, [], [] );
nice := GroupHomomorphismByImagesNC( G, K, [], [] );
SetIsBijective( nice, true );
return nice;
fi;

gens := IndependentGeneratorsOfAbelianGroup( G );
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20 changes: 20 additions & 0 deletions tst/testinstall/triviso.tst
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@@ -0,0 +1,20 @@
#############################################################################
##
#W triviso.tst
#Y Bernhard Reinke
##
#############################################################################
##

gap> START_TEST("triviso.tst");
gap> G := Group(());
Group(())
gap> phi := IsomorphismPermGroup(G);
[ ] -> [ ]
gap> HasIsBijective(phi);
true
gap> inv := InverseGeneralMapping(phi);
[ ] -> [ ]
gap> HasIsMapping(inv);
true
gap> STOP_TEST( "triviso.tst", 10000);