Dear Stefan,
can you briefly tell me what the problem is ?
Look at the file pseries.cpp. See: http://www.ginac.de/viewcvs/GiNaC/ginac/pseries.cpp?rev=1.93&view=markup . The method mul::pseries contains the code fragment. int real_ldegree = 0; try { real_ldegree = buf.expand().ldegree(sym-r.rhs()); } catch (std::runtime_error) {} if (real_ldegree == 0) { int orderloop = 0; do { orderloop++; real_ldegree = buf.series(r, orderloop, options).ldegree(sym); } while (real_ldegree == orderloop); } The do ... while loop looks for the lowest degree for which the series is nonzero. This is done for very factor in a product. Hence, if there is never going to occur a term in the series that is nonzero, there is a problem. I would like to see a solution where there is besides a series method also a method that returns the leading term, that may also return a result that says that no leading term was found up to a certain order. Best wishes, Chris