<A> bool addAndChange(Cl<A> cl, A a) {
  if (cl == null || !cl.add(a)) false;
  change();
  true;
}

void <A> clearAndChange(Cl<A> cl) {
  if (cl == null) ret;
  cl.clear();
  change();
}

ifclass LongBuffer
void addAndChange(LongBuffer buf, long a) {
  if (buf == null) ret;
  buf.add(a);
  change();
}

void clearAndChange(LongBuffer buf) {
  if (buf == null) ret;
  buf.clear();
  change();
}
endif