[GiNaC-list] problem about collect_common_factors

Hi all, I got a strange problem about collect_common_factors, the problem can be reproduced by the following example: ------ symbol a("a"),b("b"),c("c"); symtab table; table["a"] = a; table["b"] = b; table["c"] = c; parser reader(table); ex res = reader("b*((c+c*(1+4*a+2*b+b^2)-c*(1+2*b+b^2)-(1+4*a)*c))-a*(c+c*(1+4*a+2*b+b^2)-c*(1+2*b+b^2)-(1+4*a)*c)"); cout << res << endl; cout << collect_common_factors(res) << endl; ------ the collect_common_factors will throw an error: division by zero. so is this a bug for collect_common_factors? Best regards! Feng