for (int i=0; i<ls.nops(); i++) {
if (is_ex_exactly_of_type(ls.op(i),symbol)) {
for (int i=0; i<ls.nops(); i++) {
if (is_ex_exactly_of_type(ls.op(i),symbol)) {
const symbol *o = static_cast<const symbol *>(&other);
if (serial==o->serial) return 0;
return serial < o->serial ? -1 : 1;
const symbol *o = static_cast<const symbol *>(&other);
if (serial==o->serial) return 0;
return serial < o->serial ? -1 : 1;