From 8cb65f4c1e6fe9a3375de1eb9c339bfc8f4ac921 Mon Sep 17 00:00:00 2001 From: Wilf Wilson Date: Mon, 18 Jan 2021 10:26:22 +0000 Subject: [PATCH] stbcbckt: slightly optimise Intersection2 perm gps --- lib/stbcbckt.gi | 4 ++-- tst/testinstall/stbcbckt.tst | 11 +++++++++++ 2 files changed, 13 insertions(+), 2 deletions(-) create mode 100644 tst/testinstall/stbcbckt.tst diff --git a/lib/stbcbckt.gi b/lib/stbcbckt.gi index 772e274de4..6b54b383cf 100644 --- a/lib/stbcbckt.gi +++ b/lib/stbcbckt.gi @@ -2960,8 +2960,8 @@ local Omega, P, rbase, L,mg,mh,i; mh:=MovedPoints(H); Omega := Intersection(mg,mh); - # disjoint? - if Length(Omega)=0 then + # no two points moved in common? + if Length(Omega)<=1 then return TrivialSubgroup(Parent(G)); fi; diff --git a/tst/testinstall/stbcbckt.tst b/tst/testinstall/stbcbckt.tst new file mode 100644 index 0000000000..b596361eca --- /dev/null +++ b/tst/testinstall/stbcbckt.tst @@ -0,0 +1,11 @@ +#@local G,p +gap> START_TEST("stbcbckt.tst"); + +# Intersection for perm groups with a single moved point in common +gap> G := Group(GeneratorsOfGroup(SymmetricGroup(100)));; +gap> p := PermList(Concatenation([100 .. 199], [1 .. 99]));; +gap> IsTrivial(Intersection(G, G ^ p)); +true + +# +gap> STOP_TEST("stbcbckt.tst", 1);