Function: galoisisabelian
Section: number_fields
C-Name: galoisisabelian
Prototype: GD0,L,
Help: galoisisabelian(gal,{flag=0}): gal being as output by galoisinit,
 return 0 if gal is not abelian, the HNF matrix of gal over gal.gen if
 flag=0, 1 if flag is 1, and the SNF matrix of gal if flag=2.
Doc: \var{gal} being as output by \kbd{galoisinit}, return $0$ if
 \var{gal} is not an abelian group, and the HNF matrix of \var{gal} over
 \kbd{gal.gen} if $\fl=0$, $1$ if $\fl=1$, and the SNF matrix of \var{gal}
 if $\fl=2$.

 This command also accepts subgroups returned by \kbd{galoissubgroups}.
