[GAP Forum] Orbit of group action on matrices

[Benjamin Sambale]

  Dear Forum,

I've defined an action of a permutation group on a set of square 
matrices in the following way:

act:=function(x,g)
     local i;
     for i in [1..Length(x[1])] do x[i]:=Permuted(x[i],g); od;
     return Permuted(x,g);
end;

This works as expected, for example:

gap> act([[1,2],[3,4]],(1,2));
[ [ 4, 3 ], [ 2, 1 ] ]

However, using the Orbit command gives

gap> Orbit(Group((1,2)),[[1,2],[3,4]],act);
Lists Assignment: <list> must be a mutable list

What is wrong here?

Thanks,
Benjamin Sambale