Dear GAP-Forum,

Rudolf Muradian wrote:

gap> d2 := DihedralGroup(2); Size(d2);
Group( (1,2), (3,4) )
4

gap> d4 := DihedralGroup(4); Size(d4);
Group( (1,2) )
2
Is here a bug ?

Yes. The special treatment for degrees 2 and 4 went wrong. To fix it,
replace the function 'DihedralPermGroup' in the file ~gap/grp/permgrp.grp
by the following code:

#############################################################################
##
#F  DihedralPermGroup( <n> )  . . . . . . . . . .  dihedral permutation group
##
DihedralPermGroup := function ( n )
    local   D, g, h;
    if n = 2  then
        D := Group((1,2));
    elif n = 4  then
        g := (1,2);
        h := (3,4);
        D := Group( g, h );
    else
        g := PermList( Concatenation( [2..n/2], [1] ) );
        h := PermList( Concatenation( [1], Reversed( [2..n/2] ) ) );
        D := Group( g, h );
    fi;
    return D;
end;

Best regards,

Alexander Hulpke

PS.: This should also answer your two other mails. A.H.