// NotifyingList is our new go-to way to wrap a list
// with additional functions.
persistable sclass VectorSSIList extends AbstractSSIList<VectorSSI> {
  *() { init(); }
  *(Cl<? extends AbstractSSI> l) { super(l); }
  
  VectorSSI importSSI(AbstractSSI ssi) {
    ret toVectorSSI(ssi);
  }
  
  L<VectorSSI> vectorSSIs() { ret instancesOf VectorSSI(this); }
  L<VectorSSI> literalSSIs() { ret instancesOf SSI(this); }
}