Dear Martin, On Sun, 11 Feb 2007, [ISO-8859-1] Martin Sandve Aln=E6s wrote: > ex m =3D series_to_poly(s).evalm(); Can't you simply call your own C++-written tree transversal algorithm at=20 this point to check whether there actually are matrix products somewhere=20 and then only call evalm to evaluate them? Best wishes, Chris