program matrix_transposition;
    mat := [[1,2,3,4], [5,6,7,8], [9,10,11,12]];
    print(mat);
    print(' -> ');
    print(transpose(mat));

    proc transpose(m);
        return [[m(y)(x) : y in [1..#m]] : x in [1..#m(1)]];
    end proc;
end program;