Dear Chris, attached is a patch (against GiNaC 1.3.7) which should fix the problem. A few explanations: If one does a series expansion up to n of a product A*B we have to know the ldegree of B in order to determine how far we have to expand A (and vice versa). Currently the implementation finds for each factor the ldegree first, by expanding it to order 1,2,3,4,etc until a non-vanishing ldegree is found. If a factor is a complicated zero, a non-vanishing ldegree is never found and the algorithms loops for eternity. In addition, this is quite inefficient, if a factor has a large ldegree: Then this factor is expanded up to its ldegree, although we only asked for an expansion up to n. The patch splits the computation of the ldegrees into two stages: In the first stage all negative ldegrees are computed.