ex aseries = (a-a.subs(r)).series(r, order, options);
fseries = f.series(x == (a.subs(r)), order, options);
for (size_t i=0; i<fseries.nops(); ++i) {
ex aseries = (a-a.subs(r)).series(r, order, options);
fseries = f.series(x == (a.subs(r)), order, options);
for (size_t i=0; i<fseries.nops(); ++i) {