Dear all, The GiNaC feature is_polynomial() returns true in a scenario I feel is false. Namely, 1/(1-x) When running the attached code I obtain, -(-1+x)^(-1).is_polynomial(x) 1 x-(-1+x)^(-1).is_polynomial(x) 0 as output. I observed the result on two computers, MacBook Pro Darwin Kernel version 13.1.0 using GiNaC 1.6.2 64-bit DESY blade server scientific linux 2.6.18-371.1.2.el5 using GiNaC 1.6.2 Additionally, in preparing this report the following variations occurred, 1/(1-pow(x,2)) -> is polynomial 1/(1-pow(x,n)) -> is not polynomial (n being a symbol) 1/(1+x) -> is not polynomial on an SL6 installation running kernel version 2.6.32-431.20.3.el6.x86_64, gcc 4.4.7) using GiNaC 1.6.2 Yours, Mark