Function: groupisnormal
Section: combinatorics
C-Name: groupisnormal
Prototype: iGG
Help: groupisnormal(G,H): test whether the permutation group H is
 normal in GH (hence in G if H is a subgroup of G).
Doc: test whether the permutation group $H$ is normal in the group
 $GH$ (hence in $G$ if $H$ is a subgroup of $G$).
